The distinctive features and prognosis of Hodgkin's disease with initial bone marrow involvement were studied in 53 patients. This form is characterized by clinical and biological signs of rapid evolution, diffuse lymphoid tissue involvement with enlarged liver and spleen, increased lymphocyte depletion and pancytopenia--the last named being rare in other forms. Sternberg cells were found in 80% of bone marrow biopsies, often associated which fibrosis, which always disappeared during remissions. Remission was obtained with multiple chemotherapy (chiefly MOPP) in 82% of the patients and was complet in 44%. Blood toxicity was severe in cases with myelofibrosis. Relapses occurred in 14 out of 39 patients and were either local and responsive to radiotherapy or diffuse and invariably lethal. They usually took place in those lymph nodes which were most affected initially. Additional radiotherapy and courses of MOPP reduce the risk of relapse. The long-term prognosis was similar to that of other visceral forms, with a survival rate leveling off at 83% after 6 years in patients in complete remission.