Radiation-related thyroid dysfunction is a common occurrence in patients with Hodgkin's disease treated with mantle field radiation. Although chemical and clinical hypothyroidism are most commonly seen, Graves' disease has also been described. We have examined the records of 437 surgically staged patients who received mantle field irradiation between April 1969 and December 1980 to ascertain the frequency of manifestations of Graves' disease. Within this group, seven patients developed hyperthyroidism accompanied by ophthalmic findings typical of those seen in Graves' disease. The actuarial risk of developing Graves' disease at 10 years following mantle irradiation for Hodgkin's disease was 3.3% in female patients and 1% in male patients in this study. The observed/expected ratios were 5.9 and 5.1 for female and male patients, respectively. This observed risk significantly exceeded that seen in the general population.