Between April 1969, and December 1974, 111 consecutive surgically staged I A and II A patients with supradiaphragmatic Hodgkin's disease were treated at the Joint Center for Radiation Therapy. Patients received 3600--4400 rad to mantle and para-aortic--splenic pedicle regions. Median follow-up was 56 months (30--96). Fourteen patients developed relapsing Hodgkin's disease and three patients died of possible treatment-related causes, two with acute myocardial infarctions and one with radiation pneumonitis. Patients with mediastinal enlargement greater than one third of the chest diameter have a significantly higher risk (p less than 0.01) of developing relapse (9 of 18) than patients with lesser or no mediastinal disease (5 of 93). Of the 18 patients with large mediastinal disease, six relapsed in the mediastinum and two in the lung. There continue to be no pelvic extensions in the entire group. There is a 92% relapse-free and 97% overall survival in the 93 patients without extensive mediastinal disease. We continue to recommend mantle and para-aortic--splenic pedicle irradiation for these patients. In view of the large number of relapses in patients with extensive mediastinal disease, we are now treating this subgroup of patients with MOPP chemotherapy in addition to mantle and para-aortic irradiation.