We describe the histologic and immunohistochemical findings in specimens from bone marrow (BM) biopsies performed for staging purposes in 13 patients with a previous tissue-based diagnosis of T-cell-rich B-cell lymphoma (TCRBCL). Bone marrow involvement was found in 8 (62%) of 13 cases and was often paratrabecular. The histologic appearance was not pathognomonic of TCRBCL, with the differential diagnosis including Hodgkin's disease and peripheral T-cell lymphoma. The infiltrates typically had a pale low-power appearance (due to histiocytic infiltration, relative hypocellularity, or both) that, in conjunction with the presence of a polymorphous infiltrate of scattered large atypical cells amid a mixed infiltrate of small lymphocytes and histiocytes, was suggestive of Hodgkin's disease. Immunohistochemistry revealed CD20 reactivity of the large atypical cells with the absence of CD15 and CD30 reactivity, supporting the diagnosis of TCRBCL. A prominent small T-cell infiltrate accompanying the large atypical cells was observed in all positive BM biopsy specimens. The increased incidence of BM involvement in TCRBCL is significantly higher than that found in de novo B-cell diffuse large cell lymphoma, suggesting a possible biologic difference between the two entities. Our cases share some similar clinicopathologic features with histiocyte-rich B-cell lymphoma and with diffuse lymphocyte-predominant Hodgkin's disease, paragranuloma type. We discuss the possible relationship to these two entities.