Cases of adult T-cell leukemia (ATL) with aberrant phenotypes have a very poor prognosis. We report the development of acute type, CD 8 positive ATL in a carrier of hepatitis B virus (HBV). The patient was treated with a combination of lamivudine and chemotherapy and consequently had longer-term survival than those reported previously. A 64-year-old(corrected 65-year-old) man was referred to our hospital in January 2002 because of ascites and abdominal tumor. He was positive for anti-HTLV-1 antibody and HBV surface antigen. Generalized computed tomography demonstrated bilateral pleural effusion, abdominal mass, and massive ascites. Cytological examination of ascitis revealed numerous atypical lymphoid cells,which were positive for CD 2, CD 5, CD 8, and CD 25. Monoclonal integration of HTLV-1 provirus was detected by Southern blot analysis on DNA extracted from lymphoid cells. A diagnosis of acute type, CD 8 positive ATL was made. Lamivudine was administered for prevention of chemotherapy induced HBV reactivation. Subsequently, he was treated with 6 cycles of CHOP and went into remission. He maintained clinical remission during a follow-up of 13 months and then relapsed. Further salvage therapies were provided with a transient effect. He died of sepsis in February 2004. The overall survival time of this patient was 25 months. It is possible that lamivudine combined with chemotherapy may have had a therapeutic effect on ATL in this case.