Two cases of primary gastric T-cell lymphoma associated with human T lymphotropic virus type 1 (HTLV-1) are presented. Case 1 was a 54-year-old man who had multiple ulcerating tumors in the lower corpus and gastric antrum. Case 2, a 60-year-old man, showed a large ulcerating tumor in the upper corpus. Both patients were positive for serum anti-HTLV-1 antibody and for the monoclonal integration of HTLV-1 proviral DNA in the tumor cells by Southern blot analysis. The patients were thus diagnosed as having primary gastric T-cell lymphoma associated with HTLV-1 of stage II(1). Case 1 underwent total gastrectomy followed by chemotherapy, while Case 2 was treated by chemotherapy and radiotherapy. Both patients have been in complete remission for more than 4 years (96 months in Case 1 and 50 months in Case 2) after the treatments. Although primary gastric T-cell lymphomas associated with HTLV-1 is characterized by an extremely poor prognosis, the present cases suggest that in the early stage, long-term survival can possibly be achieved with appropriate treatments.