Twelve cases of non-Hodgkin's lymphoma and acute myeloblastic leukemia or one of its variants are reported. An additional 33 cases from the literature are reviewed. The mean interval between the diagnosis of lymphoma and acute leukemia is 5.2 years. In 5 patients the two diseases occurred simultaneously or within 6 months of each other. All but 10 of the 45 patients received radiation therapy for their lymphoma. Nine patients had either total nodal or total body irradiation or both. Eight patients received chemotherapy alone. No patient was untreated. Survival after the diagnosis of acute leukemia ranged from 3 days to 14 months, with a median of 3 months. Four patients achieved complete hematological remission following antileukemic therapy. Acute leukemia is estimated to occur in patients with non-Hodgkin's lymphoma in New York State with a 37-fold increased frequency over the expected number. Although acute leukemia may occur in a higher than expected frequency in patients with non-Hodgkin's lymphoma because of an increased risk of a second neoplasm in patients with a primary tumor, it seems more likely that the acute leukemia may be related to the radiotherapy and/or chemotherapy administered to treat the lymphoma. Late death from leukemia after chemotherapeutic or radiotherapeutic remission of advanced non-Hodgkin's lymphoma is preferable to morbidity and/or early death from untreated or inadequately treated lymphoma.