Since 1976, we have discovered isolated, solitary nodules in seven spleens due to reactive lymphoid hyperplasia. Six cases were encountered at staging laparotomy for malignant lymphoma and one case was observed in a spleen resected because of autoimmune hemolytic anemia. Macroscopically, the nodules were strongly suggestive of splenic involvement by lymphoma; microscopically, however, splenic lymphoma was not demonstrated in any case. In four spleens, the nodules were formed by focal aggregation of reactive germinal centers. In three other cases, the nodules were manifestations of a localized proliferation of lymphocytes, including immunoblasts and plasma cells. The immunoblasts raised the question of splenic involvement by Hodgkin's disease, but Reed-Sternberg cells were not identified. The etiology of localized splenic lymphoid hyperplasia is unknown, but the lesion is likely analogous to florid reactive follicular and diffuse hyperplasia observed in a solitary enlarged lymph node stimulating malignant lymphoma.