The records of 1,329 patients with Hodgkin's disease admitted from 1965 to 1982 were analyzed to assess the relative frequency of second neoplasms. Within a median follow-up of 9.5 years, a total of 68 new cancers were documented. Nineteen cases of acute nonlymphocytic leukemia, 6 cases of non-Hodgkin's lymphomas, and 43 cases with different types of solid tumors were identified. The overall risk of non-Hodgkin's lymphoma was 1.3% +/- 0.6% and of solid tumors was 8.3% +/- 1.5% when basal cell carcinomas were included and 6.7% +/- 1.4% when basal cell carcinomas were excluded. No cases of leukemia were documented in patients treated with radiation therapy only. The 12-year estimate of leukemia by treatment was as follows: chemotherapy only 1.4% +/- 2.3%; radiation plus MOPP (mechlorethamine, vincristine, procarbazine, and prednisone) 10.2% +/- 5.2%; radiation plus ABVD (Adriamycin, bleomycin, vinblastine, and dacarbazine) 0; and radiation plus other drug regimens 4.8% +/- 1.6%. The risk of leukemia was particularly high (15.5% +/- 7.4%) in patients who received salvage MOPP after radiation failure. A positive association was also noted between increasing age and risk of second malignancies, especially leukemia. The incidence of second neoplasms can be markedly decreased by deleting from potentially curative therapy certain drugs such as alkylating agents, procarbazine, and nitrosourea derivatives.