Fifteen patients with a rare malignant lymphoma characterized by a high content of epithelioid histiocytes are reported. This lymphoma, referred to as "Lennert's lymphoma," was originally thought to be a variant of Hodgkin's disease, but has both histologic and clinical differences. Although the infiltrate is polymorphous, diagnostic Reed-Sternberg cells are difficult to find and involvement of tonsils relatively common. Lennert's lymphoma bears some resemblance to immunoblastic lymphadenopathy in that some patients have a history of allergies, polyclonal hyperglobulinemia, and all lymph nodes demonstrate variable proliferation of immunoblasts. However, both vascular proliferation and the amorphous eosinophilic interstitial material characteristic of immunoblastic lymphadenopathy are lacking. The clinical course in this series was unpredictable with rapid death in six cases, chiefly from sepsis, 1--18 months following diagnosis despite therapy as for Hodgkin's disease. The remaining eight patients for whom follow-up data are available are in apparent clinical remission. Further cases and investigations are needed to determine the precise behavior of Lennert's lymphoma and to learn its exact status in relation to other malignant lymphomas or immunoblastic proliferations.