There has been concern that living near nuclear installations might increase the risk of cancer, including childhood leukemia, in surrounding communities. Such concern has been voiced by residents in Armstrong and Westmoreland Counties in Western Pennsylvania in conjunction with the operation of two former nuclear materials processing facilities located in the Apollo borough and the Parks township, just three miles apart. These facilities began operating in 1957 and 1960 and processed uranium and plutonium for commercial and naval applications. To evaluate the possibility of increased cancer rates in communities around the Apollo-Parks nuclear facilities, a cancer incidence and a cancer mortality survey were conducted. The county mortality findings are reported here. Nearly 40,000 cancer deaths occurred in the population residing in Armstrong and Westmoreland Counties from 1950 through 1995. Each of these two study counties was matched for comparison to three control counties in the same region on the basis of age, race, urbanization, and socioeconomic factors available from the 1990 U.S. Census. There were over 77,000 cancer deaths in the 6 control counties during the 45 y studied. Following similar methods used by the National Cancer Institute, Standardized Mortality Ratios (SMRs) were computed as the ratio of observed numbers of cancers in the study and control counties compared to the expected number derived from general population rates of the United States. Relative risks (RR) were computed as the ratios of the SMRs for the study and the control counties. There were no significant increases in the study counties for any cancer when comparisons were made with either the U.S. population or the control counties. In particular, deaths due to cancers of the lung, bone, liver, and kidney were not more frequent in the study counties than in the control counties. These are the cancers of a priori interest given that uranium and/or plutonium might be expected to concentrate in these tissues. Deaths from all cancers combined also were not increased in the study counties, and the RRs of cancer mortality before the facilities operated (1950-1964), during plant operations (1965-1980) and after plant closure (1980-1995) were similar: 0.96, 0.95 and 0.98, respectively. For childhood leukemia mortality, the relative risk comparing the study counties with their controls before plant start-up was 1.02, while during operations (RR 0.81) and after closure (RR 0.57) the relative risks were lower. The study is limited by the correlational approach and the relatively large size of the geographic areas of the counties studied.