A descriptive epidemiologic study of cancer mortality among residents of counties near the Hanford nuclear facility site in Richland, Washington, was conducted. Between 1944 and 1957, radioactive 131I was released into the environment from the Hanford site. Cancer mortality from 1950 through 2000 was evaluated in four counties with the highest estimated exposure to 131I and compared with the cancer mortality experience in five demographically similar counties in Washington State with minimal 131I exposure. Overall, cancer rates in the study counties were slightly below those in the comparison counties [relative risk (RR) 0.95; 95% confidence interval (CI) 0.93-0.97], due mainly to a low risk for lung cancer (RR 0.89; 95% CI 0.85-0.93). Thyroid cancer (n=33; RR 0.84; 95% CI 0.56-1.26), female breast cancer (n=1,233; RR 0.99; 95% CI 0.92-1.06), leukemia other than chronic lymphocytic leukemia (n=492; RR 0.95; 95% CI 0.85-1.06), and childhood leukemia (n=71; RR=1.06; 95% CI 0.78-1.43) were not significantly increased in the exposed counties. Furthermore, there was no evidence that the cancer death rates over time differed between study and comparison counties. Patterns over time of thyroid cancer in particular were similar for exposure and comparison counties. Although based on a geographic correlation design, these data suggest that living near the Hanford site has not increased cancer rates.