We examined the bone marrow biopsy of a 19-year-old male patient who had a fever for 3 months. Physical examination findings were unremarkable; blood culture results were negative. Computed tomography of the neck, chest, abdomen, and pelvis did not reveal lymphadenopathy or any other abnormality. His peripheral blood examination revealed a hemoglobin level, 9.7 g/dL; white blood cell count, 2.6×10⁹/L; and platelet count, 32×10⁹/L. The peripheral blood film showed a leukoerythroblastic picture. The bone marrow aspirate resulted in a dry tap. Bone trephine was a specimen of adequate length. The normal architecture was completely effaced. There was diffuse infiltration with pleomorphic lymphoid cells (A, B). Some cells were large; these atypically large cells showed positivity for CD20 (C) and negativity for CD15 and CD30. The small lymphocytes in the background showed positivity for CD3 (D). A diagnosis of T cell/histiocyte-rich large B-cell lymphoma was made. T cell/histiocyte-rich large B-cell lymphomas are a rare and aggressive subtype of diffuse large B-cell lymphoma. The neoplastic B cells constitute <10% of cells of the infiltrate. Primary involvement of the bone marrow in this type of lymphoma, observed in this case, is a very rare finding.