A case of a 34-year-old man with stage IIIB nodular sclerosis Hodgkin's disease complicated by the development of a central nervous system non-Hodgkin's lymphoma is described. The second tumor became symptomatic eight months after the initial diagnosis of Hodgkin's disease, but a tissue diagnosis was not made until autopsy two months later. The Hodgkin's disease was, at that time, in remission, and the autopsy revealed no persistent or recurrent Hodgkin's disease. Despite radiotherapy, the brain lymphoma had progressed to involve the spinal leptomeninges extensively, but there was no lymphoma outside the central nervous system (CNS) at autopsy. The significance of this unique case is discussed in light of the known risk for non-Hodgkin's lymphoma as a second malignancy after Hodgkin's disease and in view of recent information concerning CNS lymphoma.