The incidence of childhood malignancies in 20 areas surrounding major nuclear installations is compared with the incidence in matched control regions. The study is based on the registry of childhood malignancies in the Federal Republic of Germany and includes 1,610 cases which were diagnosed before 15 years of age from 1980 to 1990. The relative risk (RR) was 0.97 for all malignancies and 1.06 for acute leukemia in all regions within a 15 km radius of an installation. Increased RR was observed in subgroups for acute leukemia before five years of age and for lymphomas, especially in regions close to installations (less than 5 km) which started operation before 1970. Most of this increase was attributable to an unexpectedly low incidence in the control regions which could not be explained by analyzing possible confounding factors. Using the same control regions, a comparable and even more pronounced increase of RRs was observed in regions where nuclear power plants have been projected.