For the purpose of studying the histological findings and prognosis of stomach cancer in atomic bomb survivors, a histological diagnosis of 600 cases of stomach cancer observed between 1964 and 1986 in three medical institutions in Hiroshima City was made by a single pathologist and, furthermore, analysis of 231 cases thereof was performed using the DS86 dose estimated by the Radiation Effects Research Foundation. 1) By histological type of stomach cancer, the frequency of poorly differentiated adenocarcinoma (poorly differentiated adenocarcinoma and signet ring cell carcinoma) was significantly higher in the 1 rad or more group (average stomach organ dose of 30.6 rad) than in the 0 rad group. 2) As for stromal type, the frequency of scirrhous type was significantly higher in the 1 rad or more group, but no difference in infiltrative behavior could be demonstrated. 3) Early cancer tended to be observed at a low rate in the 1 rad or more group. 4) As for average survival time, of the early cancers only well differentiated adenocarcinoma showed a significantly lower survival time in the 1 rad or more group when compared to the 0 rad group.