Rural population mixing and childhood leukaemia: effects of the North Sea oil industry in Scotland,including the area near Dounreay nuclear site.

OBJECTIVE--To determine if any excess of childhood leukaemia and non-Hodgkin''s lymphoma was associated with certain striking examples of population mixing in rural Scotland produced by the North Sea oil industry. DESIGN--Details were traced for over 30,000 workers involved in the construction of the large oil terminals in the Shetland and Orkney islands in northern Scotland or employed offshore. Home addresses of the 17,160 Scottish residents were postcoded, integrated with census data, and then classified as urban or rural. Rural postcode sectors, ranked by proportion of oil workers, were grouped into three categories with similar numbers of children but contrasting densities of oil workers. The incidence of leukaemia and non-Hodgkin''s lymphoma was examined in these rural (and also in urban) categories in the periods 1974-8, 1979-83 and 1984-8. SETTING--Scotland. SUBJECTS--Young people below age 25. RESULTS--A significant excess of leukaemia and non-Hodgkin''s lymphoma was found in 1979-83 in the group of rural home areas with the largest proportion of oil workers, following closely on large increases in the workforce. The area near the Dounreay nuclear installation, where an excess of leukaemia is already well known, was within the rural high oil category. CONCLUSION--The findings support the infection hypothesis that population mixing can increase the incidence of childhood leukaemia in rural areas. They also suggest that the recent excess in the Dounreay-Thurso area is due to population mixing linked to the oil industry, promoted by certain unusual local demographic factors.     

Effect of population mixing and socioeconomic status in England and Wales, 1979-85, on lymphoblastic leukaemia in children.

OBJECTIVE: To examine the effects of migration, diversity of migrant origins, commuting, and socioeconomic status on the incidence of acute lymphoblastic leukaemia in childhood. DESIGN: Poisson regression analysis of incidence rates in relation to the variables of interest. SETTING: The 403 county districts of England and Wales during 1979-85. SUBJECTS: Children aged under 15 years. RESULTS: There were significant trends in the incidence of lymphoblastic leukaemia at ages 0-4 and 5-9 years with the proportion of children in a district who had recently entered the district. While there was no consistent relation between the proportion of recent incomers in the total population of a district and its incidence rate, the combination of higher migration with greater diversity of origins or distance moved was associated with higher incidence in both age groups. Incidence increased significantly at age 0-4 with the level of employment in a district and at age 5-9 with the proportion of households with access to a car. No significant trends were found with commuting. CONCLUSIONS: The results for level of child migration and diversity of total migration provide evidence of an effect of population mixing on the incidence of childhood leukaemia which is not restricted to areas experiencing the most extreme levels of mixing.     

Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case-control study

Objective To determine whether there is an association between distance of home address at birth from high voltage power lines and the incidence of leukaemia and other cancers in children in England and Wales.Design Case-control study.Setting Cancer registry and National Grid records.Subjects Records of 29 081 children with cancer, including 9700 with leukaemia. Children were aged 0-14 years and born in England and Wales, 1962-95. Controls were individually matched for sex, approximate date of birth, and birth registration district. No active participation was required.Main outcome measures Distance from home address at birth to the nearest high voltage overhead power line in existence at the time.Results Compared with those who lived > 600 m from a line at birth, children who lived within 200 m had a relative risk of leukaemia of 1.69 (95% confidence interval 1.13 to 2.53); those born between 200 and 600 m had a relative risk of 1.23 (1.02 to 1.49). There was a significant (P < 0.01) trend in risk in relation to the reciprocal of distance from the line. No excess risk in relation to proximity to lines was found for other childhood cancers.Conclusions There is an association between childhood leukaemia and proximity of home address at birth to high voltage power lines, and the apparent risk extends to a greater distance than would have been expected from previous studies. About 4% of children in England and Wales live within 600 m of high voltage lines at birth. If the association is causal, about 1% of childhood leukaemia in England and Wales would be attributable to these lines, though this estimate has considerable statistical uncertainty. There is no accepted biological mechanism to explain the epidemiological results; indeed, the relation may be due to chance or confounding.     

Duration of Survival of Children with Acute Leukaemia: REPORT TO THE MEDICAL RESEARCH COUNCIL FROM THE COMMITTEE ON LEUKAEMIA AND THE WORKING PARTY ON LEUKAEMIA IN CHILDHOOD

The survival times of children with acute leukaemia diagnosed in the years 1963-7 in England and Wales have been studied. The children known to have been treated by physicians specializing in the treatment of leukaemia in childhood have survived considerably longer than the others.     

Childhood leukaemia in the West Berkshire and Basingstoke and North Hampshire District Health Authorities in relation to nuclear establishments in the vicinity.

During the years 1972-85, 89 children aged 0-14 were registered with leukaemia in the West Berkshire and Basingstoke and North Hampshire District Health Authorities. Two nuclear establishments are located within the health authorities, and a third is situated nearby. Fifty of the 143 electoral wards in the two district health authorities lie wholly within, or have at least half their area lying within, a circle of radius 10 km around the establishments. In those 50 electoral wards 41 children aged 0-14 were registered with leukaemia, 28.6 registrations being expected on the basis of leukaemia registration rates in England and Wales (incidence ratio = 1.4, p less than 0.05). This excess was confined to children aged 0-4, among whom there were 29 registrations of leukaemia, 14.4 being expected (incidence ratio = 2.0, p less than 0.001). In the remaining 93 electoral wards there was a small and non-significant increase in the number of registrations of leukaemia at age 0-14 (48 observed, 40.8 expected; incidence ratio = 1.2). There was no obvious trend in the incidence of childhood leukaemia over the 14 years and the overall occurrence of the malignancy in the 143 electoral wards was consistent with a random distribution. In the surrounding Oxford and Wessex Regional Health Authorities the number of registrations of leukaemia at age 0-14 was virtually identical with that expected on the basis of registration rates in England and Wales (362 observed, 372.5 expected; incidence ratio = 1.0). These data indicate that in the two district health authorities studied there was an excess incidence of childhood leukaemia during 1972-85 in the vicinity of the nuclear establishments. In the West Berkshire and Basingstoke and North Hampshire District Health Authorities an average of 60,000 children aged 0-14 lived within a 10 km radius of a nuclear establishment each year. The normal expectation of leukaemia in these children was two cases a year, whereas the recorded incidence was three cases per year, representing one extra case of leukaemia each year among these 60,000 children.     

Increasing incidence of tuberculosis in England and Wales: a study of the likely causes.

OBJECTIVE--To examine factors responsible for the recent increase in tuberculosis in England and Wales. DESIGN--Study of the incidence of tuberculosis (a) in the 403 local authority districts in England and Wales, ranked according to Jarman score, and (b) in one deprived inner city district, according to ethnic origin and other factors. SETTING--(a) England and Wales 1980-92, and (b) the London borough of Hackney 1986-93. MAIN OUTCOME MEASURE--Age and sex adjusted rate of tuberculosis. RESULTS--In England and Wales notifications of tuberculosis increased by 12% between 1988 and 1992. The increase was 35% in the poorest 10th of the population and 13% in the next two; and in the remaining 70% there was no increase. In Hackney the increase affected traditionally high risk and low risk ethnic groups to a similar extent. In the "low risk" white and West Indian communities the incidence increased by 58% from 1986-8 (78 cases) to 1991-3 (123), whereas in residents of Indian subcontinent origin the increase was 41% (from 51 cases to 72). Tuberculosis in recently arrived immigrants--refugees (11% of the Hackney population) and Africans (6%)--accounted for less than half of the overall increase, and the proportion of such residents was much higher than in most socioeconomically deprived districts. The local increase was not due to an increase in the proportion of cases notified, to HIV infection, nor to an increase in homeless people. CONCLUSIONS--The national rise in tuberculosis affects only the poorest areas. Within one such area all residents (white and established ethnic minorities) were affected to a similar extent. The evidence indicates a major role for socioeconomic factors in the increase in tuberculosis and only a minor role for recent immigration from endemic areas.     

Childhood leukaemia and non-Hodgkin's lymphoma near large rural construction sites,with a comparison with Sellafield nuclear site.

OBJECTIVE--To determine whether population mixing produced by large, non-nuclear construction projects in rural areas is associated with an increase in childhood leukaemia and non-Hodgkin''s lymphoma. DESIGN--A study of the incidence of leukaemia and non-Hodgkin''s lymphoma among children living near large construction projects in Britain since 1945, situated more than 20 km from a population centre, involving a workforce of more than 1000, and built over three or more calendar years. For periods before 1962 mortality was studied. SETTING--Areas within 10 km of relevant sites, and the highland counties of Scotland with many hydroelectric schemes. SUBJECTS--Children aged under 15. RESULTS--A 37% excess of leukaemia and non-Hodgkin''s lymphoma at 0-14 years of age was recorded during construction and the following calendar year. The excesses were greater at times when construction workers and operating staff overlapped (72%), particularly in areas of relatively high social class. For several sites the excesses were similar to or greater than that near the nuclear site of Sellafield (67%), which is distinctive in its large workforce with many construction workers. Seascale, near Sellafield, with a ninefold increase had an unusually high proportion of residents in social class I. The only study parish of comparable social class also showed a significant excess, with a confidence interval that included the Seascale excess. CONCLUSION--The findings support the infection hypothesis and reinforce the view that the excess of childhood leukaemia and non-Hodgkin''s lymphoma near Sellafield has a similar explanation.     

Childhood respiratory infection and adult chronic bronchitis in England and Wales.

The high mortality from chronic bronchitis in England and Wales and the excess of urban over rural mortality are unexplained. On dividing England and Wales into 212 local authority areas a strong geographical relation was found between death rates from chronic bronchitis and emphysema in 1959-78 and infant mortality from bronchitis and pneumonia during 1921-5. It was concluded that this relation provided strong evidence of a direct casual link between acute lower respiratory infection in early childhood and chronic bronchitis in adult life. Regression analysis suggested that infection in early childhood had a greater influence than cigarette smoking in determining the geographical distribution of chronic bronchitis. National time trends reflected the influence of both factors. Chronic air pollution in adult life may be less important a cause of chronic bronchitis than previously supposed.     

Screening for hearing loss in childhood: a study of national practice.

A questionnaire survey of all health districts in England and Wales was carried out at the end of 1984 to document screening programmes for identifying hearing loss in childhood. The response rate was 81.3%. All districts performed distraction testing, all but nine aiming at doing so at 7-9 months of age. All districts tested children''s hearing at school, generally before 7 years of age. The number of times that children were screened both before school and at school varied considerably, from one to six times before school and one to six times at school. Few districts collected information that would allow them to make judgments about the efficiency of effectiveness of their screening programmes.     

Prognostic implications of chromosomal findings in acute lymphoblastic leukaemia at diagnosis.

Chromosomes were studied on diagnostic bone-marrow samples from 39 children with acute lymphoblastic leukaemia (ALL). The patients were classified, according to the chromosomal characteristics of the major proportion of their leukaemia cells, into five categories; hyperdiploid, pseudodiploid, diploid, hypodiploid, and mixed. Patients in the hyperdiploid category had significantly longer first remissions than those in all other categories, and those in the pseudodiploid category had the shortest. Neither the absence of any normal cells nor the presence of detectable clones appeared to be an adverse feature. We suggest that the proportion of hyperdiploid cells, determined by conventional chromosomal staining techniques, may be used as an additional prognostic feature in childhood ALL.     

Distribution of childhood leukaemias and non-Hodgkin's lymphomas near nuclear installations in England and Wales.

OBJECTIVE--To examine the relation between the risk of childhood leukaemia and non-Hodgkin''s lymphoma and proximity of residence to nuclear installations in England and Wales. DESIGN--Observed and expected numbers of cases were calculated and analysed by standard methods based on ratios of observed to expected counts and by a new statistical test, the linear risk score test, based on ranks and designed to be sensitive to excess incidence in close proximity to a putative source of risk. SETTING--Electoral wards within 25 km of 23 nuclear installations and six control sites that had been investigated for suitability for generating stations but never used. SUBJECTS--Children below age 15 in England and Wales, 1966-87. MAIN OUTCOME MEASURE--Registration of any leukaemia or non-Hodgkin''s lymphoma. RESULTS--In none of the 25 km circles around the installations was the incidence ratio significantly greater than 1.0. The only significant results for the linear risk score test were for Sellafield (P = 0.00002) and Burghfield (P = 0.031). The circles for Aldermaston and Burghfield overlap; the incidence ratio was 1.10 in each. One of the control sites gave a significant linear risk score test result (P = 0.020). All the tests carried out were one sided with P values estimated by simulation. CONCLUSION--There is no evidence of a general increase of childhood leukaemia or non-Hodgkin''s lymphoma around nuclear installations. Apart from Sellafield, the evidence for distance related risk is very weak.     

The 1918-1919 influenza pandemic in England and Wales: spatial patterns in transmissibility and mortality impact

Spatial variations in disease patterns of the 1918-1919 influenza pandemic remain poorly studied. We explored the association between influenza death rates, transmissibility and several geographical and demographic indicators for the autumn and winter waves of the 1918-1919 pandemic in cities, towns and rural areas of England and Wales. Average measures of transmissibility, estimated by the reproduction number, ranged between 1.3 and 1.9, depending on model assumptions and pandemic wave and showed little spatial variation. Death rates varied markedly with urbanization, with 30-40% higher rates in cities and towns compared with rural areas. In addition, death rates varied with population size across rural settings, where low population areas fared worse. By contrast, we found no association between transmissibility, death rates and indicators of population density and residential crowding. Further studies of the geographical mortality patterns associated with the 1918-1919 influenza pandemic may be useful for pandemic planning.     

Risk of acute childhood leukaemia in Sweden after the Chernobyl reactor accident. Swedish Child Leukaemia Group.

OBJECTIVE--To evaluate the risk of acute childhood leukaemia in areas of Sweden contaminated after the Chernobyl reactor accident in April 1986. DESIGN--Population based study of childhood leukaemia diagnosed during 1980-92. SETTING--Coordinates for places of residence of all 1.6 million children aged 0-15 years; aerial mapped areas of Sweden heavily contaminated after the Chernobyl accident. SUBJECTS--888 children aged 0-15 years with acute leukaemia diagnosed in Sweden during 1980-92, identified with place of birth and residence at diagnosis. MAIN OUTCOME MEASURES--Risk of leukaemia in areas contaminated after the Chernobyl accident compared with the rest of Sweden and in the same areas before the accident. RESULTS--During six and a half years of follow up after the accident the odds ratio for acute leukaemia was 0.9 (95% confidence interval 0.6 to 1.4) in highly contaminated areas (> or = 10 kBq/m2) compared with the same areas before the accident. For the subgroup acute lymphoblastic leukaemia in children aged under 5 years at diagnosis the odds ratio was 1.5 (0.8 to 2.6). For all cases diagnosed after May 1986 in highly contaminated areas compared with areas of low contamination the odds ratio was 0.9 (0.7 to 1.3). For acute lymphoblastic leukaemia in children aged under 5 years at diagnosis the odds ratio was 1.2 (0.8 to 1.9) in highly contaminated areas compared with areas of low contamination. Dose-response analysis showed no correlation between the degree of contamination and the incidence of childhood leukaemia. CONCLUSION--There has been no significant increase in the incidence of acute childhood leukaemia in areas of Sweden contaminated after the Chernobyl reactor accident.     

Seasonal variation and time trends in childhood asthma in England and Wales 1975-81.

In England and Wales hospital admissions for childhood asthma almost trebled over the period 1975-81. This may have reflected a true increase in the incidence of acute asthma, a swing from primary to hospital care, or both. The trend was not due to a change in diagnostic fashion. Monthly admissions showed a pronounced seasonal variation with fewest admissions in winter, rising in spring and early summer to peak in the autumn. A deep admission trough was present in August. The monthly admission profile was very similar throughout England and Wales, suggesting that major "trigger" factors were responsible.     

Cancer in Cumbria and in the vicinity of the Sellafield nuclear installation, 1963-90.

OBJECTIVE--To reappraise the epidemiological findings reported by the Black Advisory Group concerning a possible excess of malignant disease, particularly of childhood acute lymphoid leukaemia and non-Hodgkin lymphomas, in the vicinity of the Sellafield nuclear installation, and to determine whether any excess of malignant disease had occurred among people aged 0-24 years in the area in the years after the Black report--that is, from 1984 to 1990. DESIGN--Calculation of incidence of cancer using data from population based cancer registries and special surveys. SETTING--England and Wales; county of Cumbria; county districts Allerdale and Copeland within Cumbria; Seascale ward within Copeland. SUBJECTS--All residents under the age of 75 years in the above areas, but with particular reference to those aged 0-24 years. MAIN OUTCOME MEASURES--Numbers of cases and incidence particularly of lymphoid leukaemia and non-Hodgkin lymphomas in those aged 0-24 years, but including other cancers and age groups. RESULTS--Previous reports of an increased incidence of cancer, especially of leukaemia, among those aged 0-24 years in Seascale during the period up to and including 1983 are confirmed. During 1984-90 there was an excess of total cancer among those aged 0-24 years. This was based on four cases including two cases of non-Hodgkin lymphoma but none of leukaemia. There was an increased, but nonsignificant, incidence of other cancers, based on two cases (one pinealoma and one Hodgkin''s disease) occurring among those aged 15-24 years during 1984-90. This was not observed in the younger age group or in previous years. For the immediately surrounding area--that is, the county districts of Allerdale and Copeland excluding Seascale and in the remainder of Cumbria--there was no evidence of an increased incidence of cancer among those aged 0-24 years in either period. CONCLUSIONS--During 1963-83 and 1984-90 the incidence of malignant disease, particularly lymphoid leukaemia and non-Hodgkin lymphomas, in young people aged 0-24 in Seascale was higher than would be expected on the basis of either national rates or those for the surrounding areas. Although this increased risk is unlikely to be due to chance, the reasons for it are still unknown.     

Quality of life assessment of growth hormone deficiency in adults (QoL-AGHDA): comparison of normative reference data for the general population of England and Wales with results for adult hypopituitary patients with growth hormone deficiency

BACKGROUND/AIM: Age- and gender-specific reference values for the quality of life (QoL) measures used in assessing the impact of growth hormone deficiency (GHD) are important. The objective of this study was to develop such data for the QoL-AGHDA instrument for the population of England and Wales and to demonstrate the QoL deficit in patients with GHD. METHODS: For the purpose of this study, a questionnaire was developed that contained the EurQoL EQ-5D, QoL-AGHDA, questions recording an individual's general situation and social functioning, and a self-reported five-point rating scale of general health. The questionnaire was mailed out to a sample of 1,190 individuals drawn from the general population of England and Wales. Corresponding data for 836 patients were retrieved from KIMS (Pfizer International Metabolic Database). The postal survey data were weighted to ensure that they were representative of the general population. RESULTS: The mean weighted QoL-AGHDA scores for the general population were 6.2 and 7.1 for men and women, respectively, compared with 13.6 and 15.7 for patients. For both males and females the differences in mean QoL-AGHDA scores between the general population and patients were statistically significant for all age categories (p < 0.01). In the general population the mean QoL-AGHDA score for each category of self-assessed health status increased progressively, indicating a poorer QoL as health status declined. CONCLUSIONS: This study reports QoL-AGHDA normative values for the population of England and Wales and confirms the extent of QoL impairment in patients with GHD in comparison with the general population.     

Sub-National Targeting of Seasonal Malaria Chemoprevention in the Sahelian Countries of the Nouakchott Initiative

Background

Seasonal malaria chemoprevention (SMC) has been shown to be highly efficacious against clinical malaria in areas where transmission is acutely seasonal. SMC targeting depends on a complex interplay of climate, malaria transmission and population distribution. In this study a spatial decision support framework was developed to identify health districts suitable for the targeting of SMC across seven Sahelian countries and northern states of Nigeria that are members of the Nouakchott Initiative.

Methods

A spatially explicit decision support framework that links information on seasonality, age-structured population, urbanization, malaria endemicity and the length of transmission season was developed to inform SMC targeting in health districts. Thresholds of seasonality, population and receptive risks were defined to delineate SMC suitable health districts and define the age range of children for targeting. Numbers of children were then computed for the period 2015–2020 in SMC districts. For 2015, this was combined with maps of length of malaria transmission seasons and WHO recommended treatment regimen to quantify the number of tablets required across the SMC health districts.

Results

A total of 597 Sahelian health districts were mapped, out of which 478 (80.1%) were considered suitable for SMC based on seasonality and endemicity thresholds. These districts had an estimated 119.8 million (85%) of the total population in 2015. In the six years from 2015–2020, it is estimated that a total of 158 million children 3m to <5 years, 121 million of whom were in rural areas, will need SMC to achieve universal coverage in the Sahel. If the upper age limit of SMC targeted children was increased to <10 years in low transmission districts, a total 177 million overall, of whom 135 million were rural children, will require chemoprevention in 2015–2020. In 2015 alone, an estimated 49–72 million SP tablets and 148–217 million AQ tablets will be needed to cover all or rural children respectively under the different scenarios of upper age limits.

Conclusions

Our proposed framework provides a standardised approach to support targeting and scale up of SMC by the countries of the Nouakchott Initiative. Our analysis suggests that the vast majority of the population in this region are likely to benefit from SMC and substantial resources will be required to reach universal coverage each year.     

Response of Reticulitermes flavipes (Isoptera: Rhinotermitidae) to disturbance in laboratory arenas at different temperatures and soldier proportions

This study examined the evacuation response of groups of Reticulitermes flavipes (Kollar) workers after disturbance in laboratory arenas across a range of temperatures (16, 21, and 27 degrees C) and soldier proportions (1, 3, and 5%). Groups of workers and soldiers were disturbed in a central chamber and then monitored during a 5-d period to examine the percentage that initially evacuated, percentage of evacuees that returned, time to evacuate, time to return, and rates (percentage per hour) of evacuation and return between different temperatures and between soldier levels. Disturbance response patterns were observed that generally consisted of partial evacuation followed by movement back into disturbed areas. General alarm responses were observed and initiated specific alarm responses that resulted in more termites eventually returning to disturbed areas than originally evacuated. The typical evacuation response was not observed in groups with 5% soldiers. Instead, clustering in disturbed areas replaced evacuation. Regression revealed significant correlations between temperature and evacuation time, return time, evacuation rate, and return rate, indicating that R. flavipes alarm behaviors are influenced by temperature. There was a significant correlation between soldier proportions and the percentage of evacuees returning to disturbed areas. Analysis of variance (ANOVA) revealed significant differences between temperatures in the time to evacuate, evacuation rate, time to return, and return rate. ANOVA also showed significant differences between soldier proportions in the mean percentage of evacuees from and the rate of return to disturbed areas. Our results demonstrate that temperature influences the rate, but not the magnitude, of alarm response, whereas the influence of soldiers may not be as important in the context of general alarm as specific alarm.     

Trends in childhood leukaemia in the Nordic countries in relation to fallout from atmospheric nuclear weapons testing.

OBJECTIVE--To obtain further information about the risks of childhood leukaemia after exposure to ionising radiation at low doses and low dose rates before or after birth or to the father''s testes shortly before conception. DESIGN--Observational study of trends in incidence of childhood leukaemia in relation to estimated radiation exposures due to fallout from atmospheric nuclear weapons testing during the 1950s and 1960s. SETTING--Nordic countries. SUBJECTS--Children aged under 15 years. MAIN OUTCOME MEASURES--Incidence rates of leukaemia by age at diagnosis, sex, country, and calendar year of diagnosis or year of birth; exposure category; relation between leukaemia and exposure for children aged 0-14 and 0-4 separately. RESULTS--During the high fallout period the average estimated dose equivalent to the fetal red bone marrow was around 140 mu Sv and the average annual testicular dose 140 mu Sv. There was little evidence of increased incidence of leukaemia among children born in these years. Doses to the red bone marrow of a child after birth were higher, and during the high exposure period children would have been subjected to an additional dose equivalent of around 1500 mu Sv, similar to doses received by children in several parts of central and eastern Europe owing to the Chernobyl accident and about 50% greater than the annual dose equivalent to the red bone marrow of a child from natural radiation. leukaemia incidence and red marrow dose was not related overall, but rates of leukaemia in the high exposure period were slightly higher than in the surrounding medium exposure period (relative risk for ages 0-14: 1.07, 95% confidence interval 1.00 to 1.14; for ages 0-4: 1.11, 1.00 to 1.24). CONCLUSIONS--Current predicted risks of childhood leukaemia after exposure to radiation are not greatly underestimated for low dose rate exposures.     

Fallout from Chernobyl and incidence of childhood leukaemia in Finland, 1976-92.

OBJECTIVE--To assess effects of fallout from Chernobyl on incidence of childhood leukaemia in Finland. DESIGN--Nationwide cohort study. External exposure measured for 455 Finnish municipalities with instruments driven 19,000 km throughout the country. Values specific to municipalities corrected for shielding due to houses and fallout from A bomb testing. Internal exposure estimated from whole body measurements on a random sample of 81 children. Mean effective dose for two years after incident calculated from these measurements. Data on childhood leukaemia obtained from Finnish cancer registry and verified through hospitals treating childhood cancers. SETTING--Finland, one of the countries most heavily contaminated by the Chernobyl accident; the population was divided into fifths by exposure. SUBJECTS--Children aged 0-14 years in 1976-92. MAIN OUTCOME MEASURES--Standardised incidence ratio of childhood leukaemia and relative excess risk of childhood leukaemia per mSv. From incidence data of Finnish cancer registry for 1976-85, expected numbers specific to sex and age group (0-4, 5-9, and 10-14 years) were calculated for each municipality for three periods (1976-85, 1986-8, and 1989-92) and pooled as exposure fifths. Dose response was estimated as regression slope of standardised incidence ratios on mean doses for fifths for each period. RESULTS--Population weighted mean effective doses for first two years after the accident were 410 microSv for the whole country and 970 microSv for the population fifth with the highest dose. In all Finland the incidence of childhood leukaemia did not increase 1976-92. The relative excess risk 1989-92 was not significantly different from zero (7% per mSv; 95% confidence interval -27% to 41%). CONCLUSIONS--An important increase in childhood leukaemia can be excluded. Any effect is smaller than eight extra cases per million children per year in Finland. The results are consistent with the magnitude of effect expected.