As a follow-up to the two previous surveys of radiation therapy among the atomic bomb survivors, a large-scale survey was performed to document (1) the number of radiation therapy treatments received by the atomic bomb survivors and (2) the types of radiation treatments conducted in Hiroshima and Nagasaki. The previous two surveys covered the radiation treatments among the Radiation Effects Research Foundation Adult Health Study (AHS) population, which is composed of 20,000 persons. In the present survey, the population was expanded to include the Life Span Study (LSS), including 93,611 atomic bomb survivors and 26,517 Hiroshima and Nagasaki citizens who were not in the cities at the times of the bombings. The LSS population includes the AHS population. The survey was conducted from 1981 to 1984. The survey teams reviewed all the medical records for radiation treatments of 24,266 patients at 11 large hospitals in Hiroshima and Nagasaki. Among them, the medical records for radiation treatments of 1556 LSS members were reviewed in detail. By analyzing the data obtained in the present and previous surveys, the number of patients receiving radiation therapy was estimated to be 4501 (3.7%) in the LSS population and 1026 (5.1%) in the AHS population between 1945-1980. During 1945-1965, 98% of radiation treatments used medium-voltage X rays, and 66% of the treatments were for benign diseases. During 1966-1980, 94% of the radiation treatments were for malignant neoplasms. During this period, 60Co gamma-ray exposure apparatus and high-energy electron accelerators were the prevalent mode of treatment in Hiroshima and in Nagasaki, respectively. The mean frequency of radiation therapy among the LSS population was estimated to have been 158 courses/year during 1945-1965 and 110 courses/year during 1966-1980. The present survey revealed that 377 AHS members received radiation therapy. The number was approximately twice the total number of cases found in the previous two surveys. Thus the data on radiation therapy in the AHS members have been updated well by this survey, and will provide information for more precise dose-response analyses of radiation effects in the AHS population. The information extracted from the medical records of the hospitals consisted of hospital names, treatment periods, body sites treated, diagnoses, treatment doses, radiation sources, the field sizes of the exposures and the data for identification of the patients. These data will be essential in estimating the organ doses from scattered radiation and in evaluating the effects of therapeutic radiation.