Parathyroid tumors in A-bomb survivors in Hiroshima have been studied. Thirteen cases of parathyroid tumor were confirmed from 4,136 autopsy cases between 1961 to 1977, and an elevated incidence of tumor with increase of dose (T65D) was demonstrated (P less than 0.01). A high proportion of 42.9%, 6 out of 14 parathyroid tumors extirpated at Hiroshima University Hospital between 1956 and 1988, were atomic bomb survivors exposed within 4.1 km from the hypocenter. From an epidemiological study using 23 parathyroid tumor cases detected in Hiroshima Prefecture between 1974 and 1987, an elevated incidence of parathyroid tumors with increase of dose (proximally exposed, other exposed and control nonexposed) was demonstrated (P less than 0.001).