Trisomy 3 has been reported to be associated with marginal zone B-cell lymphoma. However, its occurrence and significance in other B-cell chronic lymphoproliferative disorders has not been fully defined. We report five cases of B-cell chronic lymphoproliferative disorders showing gain of chromosome 3 or 3q. The patients were elderly males who presented with splenomegaly with or without hepatomegaly and lymphadenopathy. The diagnoses included chronic lymphocytic leukemia (3 cases), prolymphocytic leukemia (1 case), and Waldenstrom macroglobulinemia (1 case). Distinctive feature in this group of patients was the plasmacytoid appearance of the leukemic lymphocytes, with an associated IgM hypergammaglobulinemia in three patients. The relationship between the gain of chromosome 3 and plasmacytoid differentiation in B-cell chronic lymphoproliferative disorders is discussed.