We describe nine patients who initially developed non-Hodgkin's lymphoma and subsequently developed Hodgkin's disease. The median interval from the diagnosis of non-Hodgkin's lymphoma (NHL) to the diagnosis of Hodgkin's disease (HD) was 5 years (range, 2-12 years). The median age of the patients at time of diagnosis of NHL was 54 years (range, 27-81 years). Seven of nine cases (78%) of NHL were primarily nodal. According to the Working Formulation, seven NHL were follicular (two small cleaved cell, three mixed small and large cell, two large cell), one was diffuse large cell, and one was large cell immunoblastic. All NHL had histologic or immunophenotypic findings indicative of B-cell lineage. Seven of the nine patients were treated in a nonuniform manner: four with chemotherapy and three with chemotherapy and radiation therapy. At the time of HD, the median age of the patients was 59 years (range, 35-85 years). Lymph nodes were involved in all patients. Six HD biopsies were subclassified as nodular sclerosis, one as mixed cellularity, and two cases were not further subclassified. Immunophenotypic studies revealed that the Reed-Sternberg and Hodgkin cells were LeuM1 or BerH2 positive and LCA negative in eight of nine biopsies, supporting the histologic diagnosis. These results further demonstrate that patients with NHL may subsequently develop HD. The NHLs are usually of B-cell lineage. The results also emphasize the need for rebiopsy in patients with NHL who experience an apparent clinical relapse.