Human immunodeficiency virus-associated Hodgkin lymphoma frequently involves the bone marrow and is usually recognized at staging after Hodgkin lymphoma diagnosis on a lymph node or other tissue biopsies, but occasionally the marrow involvement is the only apparent manifestation of disease. In the latter setting, diagnosis can be problematic. From a total of 42 patients with newly diagnosed human immunodeficiency virus-associated Hodgkin lymphoma, 22 subjects had positive marrow involvement at diagnosis; 16 of them had additional substantial histological and/or clinical extramedullary Hodgkin lymphoma. In the remaining 6 patients the bone marrow was the only site of disease at diagnosis. In all six cases, bone marrow biopsy revealed obvious lymphomatous involvement. Reed-Sternberg cells were identified both morphologically and immunophenotypically in all cases. Spared marrow tissue consistently showed fibrosis. All patients were males with a median age of 35 years (range, 31-58 years). All presented with fever, blood cytopenias, and severe CD4+ lymphocyte depletion (median, 70 cells/mm(3)). After diagnosis, all staging procedures were negative, and all patients were treated with chemotherapy. Median survival was 4 months (range, 2-118 mo). Longer survival was achieved in the patients who completed chemotherapy regimens; three subjects, however, died shortly before the full completion of chemotherapy, two of them from Hodgkin lymphoma. Isolated bone marrow HIV-associated Hodgkin lymphoma may be an underestimated condition in HIV-infected patients; in those individuals with unexplained fever and blood cytopenias, bone marrow biopsy should be performed with the aim of assessing for Hodgkin lymphoma, even in the absence of nodal and visceral lymphomatous involvement. A rapid diagnosis of isolated bone marrow HIV-associated Hodgkin lymphoma could expedite therapy.