Patients who have been treated for Hodgkin's disease are at increased risk for second malignant neoplasms, particularly acute nonlymphoblastic leukemia and non-Hodgkin's lymphoid malignant neoplasms (NHLMs). We diagnosed five cases of NHLM in 242 patients initially treated for Hodgkin's disease between 1973 and 1980, giving a minimum incidence for this occurrence of 2.1%. The initial therapy for Hodgkin's disease, irradiation in three patients and chemotherapy in two patients, resulted in a complete remission in each case. The NHLM appeared 12, 13, 26, 30, and 54 months after the diagnosis of Hodgkin's disease. The cell type of NHLM and immunologic phenotype were as follows: large cell, immunoblastic T; large cell, immunoblastic null; large cell, cleaved and noncleaved B; large cell, cleaved and noncleaved (not studied); and lymphoblastic T. A review of 24 other cases of NHLMs, occurring in patients treated for Hodgkin's disease, reported in the literature, confirm the morphologic and immunologic heterogeneity. The poor response to therapy in our patients and those previously described demonstrate the seriousness of this phenomenon.