Abstract This is the second report of histiocyte-rich B-cell lymphoma and the first case analyzed by flow cytometry and cytogenetic study. The immunophenotype determined by flow cytometry was that of a B-cell antigen-positive, surface immunoglobulin-negative B-cell lymphoma with 79% CD11c positive histiocytes. The lymphoid cells were composed of 76% neoplastic B-cells and 24% reactive T-cells. Immunohistochemical staining showed large numbers of histiocytes positive for CD68 and lysozyme in the lymph node and the bone marrow. Neoplastic lymphoid cells were positive for CD2O, CD45, CD74 and CDw75. The monoclonality of the tumor cells was established by the evidence of rearrangements of the heavy chain and kappa light chain genes and a complex clonal cytogenetic abnormalities including t(8;14) (gl1;g32). The tumor cells were large, pleomorphic lymphoid cells and showed no features resembling those of the L/H cells of Hodgkin's disease as previously reported. The rapidly progressive clinical course in the present case is consistent with the clinical features shown in the original study. The histiocytic component in this tumor is presumably recruited by a lymphokine with the nature of a growth factor from the tumor cells that may also be responsible for the rapid proliferation of the tumor cells and the aggressive clinical course. This entity merits special recognition because it leads to a predictable poor prognosis and because of its potential of being misdiagnosed as true histiocytic lymphoma.