A 63-year-old man complained of high fever, epigastralgia, and severe cytopenia in June, 2005. Upper gastroduodenal endoscopy revealed a gastric tumor in the greater curvature of the body. Biopsy specimens showed the infiltration of medium-sized abnormal cells. Bone marrow biopsy also indicated infiltration of the medium-sized abnormal cells. Immunophenotyping with abnormal cells was positive for CD 3, negative for CD 20 and cytokeratin. Serum investigation showed human T-cell lymphotropic virus-1 (HTLV-1) antibody below 16 fold. The diagnosis was HTLV-1 unassociated primary gastric T-cell lymphoma with bone marrow infiltration. After undergoing oral chemotherapy with VP-16 at 25 mg/day, combination chemotherapy was initiated with vincristine 2 mg/day and dexamethasone 48 mg/day. The man died with the aggressive clinical course after combination chemotherapy.