To determine if low-dose involved field radiation after complete remission induction with chemotherapy is effective in preventing relapse and improving survival in patients with stage III or IV Hodgkin disease. A randomized, controlled trial with a median follow-up time of 8.1 years. A Southwest Oncology Group multi-institutional study. Patients were entered from university- and community-based practices. 278 adults with clinical or pathologic stage III or IV Hodgkin disease, who achieved complete responses after 6 cycles of MOP-BAP (nitrogen mustard, vincristine, prednisone, bleomycin, doxorubicin, and procarbazine) and who agreed to be randomly assigned to either radiation or no further treatment. Patients were assigned to either no further treatment or low-dose radiation to all initially involved sites (radiation dose, 2000 cGy to lymph node areas and 1000 to 1500 cGy to other involved organ sites). Differences in remission duration, relapse-free survival, and survival. Remission duration, relapse-free survival, and overall survival were similar for the two groups (P = 0.09, P > 0.2, and P = 0.14, respectively). Factors that predicted shorter remission duration in a multivariate analysis were nodular sclerosis histology, bulky disease, and receipt of less than 85% of planned chemotherapy. Low-dose radiation improved remission duration in the subgroups of patients with nodular sclerosis and bulky disease. For the 169 patients with nodular sclerosis, the 5-year remission-duration estimate was 82% for the low-dose radiation group and 60% for the no further treatment group (P = 0.002). For all patients with bulky disease, the 5-year remission-duration estimate was 75% for the low-dose radiation group and 57% for the no further treatment group (P = 0.05). No difference in overall survival was noted between low-dose radiation and no further treatment in all patients or major subgroups. The 5-year survival was 86% for all patients who had a complete response as well as for patients in the nodular sclerosis subgroup. Low-dose involved field radiation after MOP-BAP chemotherapy in patients with stage III or IV Hodgkin disease did not prolong remission duration or overall survival in randomized patients. However, remission duration was prolonged in several subgroups of patients, most prominently in those with nodular sclerosis histology.