The initial promising results with alternating chemotherapy regimens (mechlorethamine, vincristine, procarbazine, and prednisone/doxorubicin, bleomycin, vinblastine, and dacarbazine [MOPP/ABVD]; lomustine, melphalan, and vindesine [CAD] plus MOPP plus ABV) combined with intermediate-dose radiation therapy (RT) have been sustained with further follow-up; 82.2% of patients (152 of 185) achieved a complete remission (CR), and overall survival is 71.7% +/- 4.4% at 8 years (median follow-up is 55 months among the survivors). No statistically significant differences were found in CR percentage, CR duration, or survival between stages IIB, IIIB, and IV patients. For that reason, stepwise Cox regression analyses to identify the important prognostic factors were performed on overall survival, tumor mortality, freedom from disease progression, and survival following disease progression. Pretreatment characteristics were also tested for association with the probability of achieving CR, CR duration, and death due to other causes. Characteristics that were consistently associated with an independently unfavorable prognosis were low hematocrit, high serum lactic acid dehydrogenase (LDH), age more than 45 years, inguinal node involvement, mediastinal mass greater than .45 of the thoracic diameter, and bone marrow involvement. Patients with two or more unfavorable characteristics were much more likely to fail treatment (median survival, 62.4 months) than those with none or only one unfavorable factor (greater than 95% survival). This striking difference between the low- and high-risk groups remained even if the comparison was restricted to patients less than or equal to 45 years of age. These results provide a basis for selecting the young patients at high risk of failure for more intensive initial treatment with either autologous bone marrow rescue or hematopoietic growth factors.