The features and prognosis of Hodgkin's disease with bone marrow involvement were studied in a series of 53 patients. This form of the disease is characterized by the high incidence of clinical and biological signs reflecting disease activity, common cytopenia (which is rare in other forms), an increased incidence of the lymphocyte depletion histologic type, and extensive lymphoid involvement, often with splenomegaly. In bone marrow biopsy specimens, Sternberg-Reed cells are found in 80% of cases and fibrosis is common, though it always disappears if remission is achieved. Chemotherapy, essentially with the MOPP combination, produced an 82% remission rate with 44% complete remission (CR). Hematologic toxicity was relatively severe in patients with marrow fibrosis. Recurrence occurred in 14 of the 39 remissions and was either localized and successfully treated by complementary radiotherapy, or diffuse and beyond any form of therapy. In nine cases, the first sign of recurrence was observed in the lymph node group initially most affected. Among the 18 patients treated by reinduction chemotherapy, four recurrences were observed. However, there was only one recurrence among the 12 patients who achieved CR and none among those who had received complementary radiotherapy. The long-term prognosis is similar to that of other visceral forms, and if CR is achieved the chance of maintaining the remission is 83% after the first year, with a follow-up exceeding 6 years.