We report a case of extranodal T-cell lymphoma with fever, hepatosplenomegaly, pancytopenia, and diffuse sinusoidal infiltration of the spleen, liver, and bone marrow by the tumor cells, mimicking malignant histiocytosis. This is the second case of T-gamma (T-cell suppressor) lymphoma resembling the case reported by Kadin et al. [N Engl J Med 304:648, 1981]. The lack of lymph node involvement in this case supports the theory that this type of lymphoma arises in the spleen. This paper draws attention to the extranodal T-cell lymphoma groups that mimic malignant histiocytosis and the need of immunophenotyping for a correct diagnosis. The causes for the absence of T-cell receptor gene rearrangement in T-cell tumors are discussed.