A 59-year-old man presented with lymphocytosis with huge splenomegaly. The abnormal lymphocytes had a high nucleoplasm:cytoplasm ratio, a prominent nucleolus and hairy cytoplasmic projections. Immunophenotyping revealed B-cell leukemia with negative reactions to CD5 and CD25. Cytogenetic study showed 46,XY,der(5)t(5;6)(q35;p21), del(7)(p13)/46,idem,add(22)(q13). The patient did not respond to chlorambucil and a combination of cyclophosphamide, vincristine and prednisolone. Splenic irradiation induced partial remission. He developed progressive anemia and thrombocytopenia and died of Escherichia coli septicemia 33 months after the diagnosis of hairy cell leukemia variant.