Three patients initially diagnosed with Hodgkin's disease developed non-Hodgkin's lymphoma 1.5, 7, and 16 years later, respectively. Combined modality therapy had been employed in one patient; the other two had received combination chemotherapy. All three of the second neoplasms were morphologically characterized as peripheral T-cell lymphomas. Cell surface marker studies performed on two of these tumors confirmed their T-cell origin. Second lymphoproliferative malignancies are an increasingly recognized complication in patients with Hodgkin's disease. Further immunologic phenotyping is needed to more conclusively define the origin and frequency of occurrence of these tumors.