A 71-year-old woman presented with malaise, skin bruising, epistaxis, and gingival bleeding of recent and prompt onset. There was no adenopathy. The liver and spleen were not enlarged. Bone marrow aspirate showed a polymorphous infiltration with lymphocytes (22%), typical Marschalko plasma cells (16%), plasmacytoid lymphocytes (29%), lymphoblasts (8%), and immunoblasts (13%). The immunoblasts morphologically resembled lymphosarcoma cells with a frequent "clover-leaf" appearance. An IgM paraprotein concentration in serum was 38.5 g/L. The bone marrow histopathology confirmed the presence of heterogenous cell infiltration, with 30% of the population being comprised of lymphoblasts and immunoblasts. In order to differentiate a polymorphous variant of Waldenström macroglobulinemia (WM) from the more common small cell lymphocytic lymphoma (SLL) in anaplastic metamorphosis, flow cytometric studies were performed on marrow specimens. A typically bright surface IgM (lambda) was demonstrated with a less bright CD38. Further immunophenotype was HLA-DR+, CD19+, CD20+ and CD10-, CD22-, T-Ag- and kappa light chain- expression. This corroborated the diagnosis of an extremely rare, polymorphous variant of WM. The marrow cytogenetics disclosed 50% (10/20) pathologic metaphases 48,X,dup(X)(p21p22),der(2), +5,del(6)(q11q21), +12,inv(16)(p13q22), del(17) (p12), and 50% normal metaphases. The patient was treated with a LOPP protocol. She failed to respond and died 5 months after the diagnosis with myocardial and renal insufficiency complicating a pronounced pancytopenia in the peripheral blood.