A 70-year-old woman was admitted to our hospital for treatment of abdominal tumor. She had complained of left abdominal pain, body weight loss and slight fever. Upper gastrointestinal endoscopy revealed on profounding ulcerous and upheaval lesion from the upper part of gastric body to the antrum. The pathological diagnosis of the biopsy specimens was T-cell lymphoma and proviral DNA (GAG) of HTLV-I was demonstrated in the biopsy specimens. Although the patient was serologically positive for anti-human T-lymphotrophic virus type I (HTLV-I) antibody, there were no leukemia/lymphoma cells in the peripheral blood or systemic lymphadenopathy. Primary gastric Adult T-cell leukemia/lymphoma (ATLL) was diagnosed. Although she received chemotherapy, the response was poor. The prognosis of lymphoma-type ATL is known to be extremely poor. This disease is frequent in aged people. Although gastrointestinal involvement is frequent in ATLL, primary gastric ATLL is rare. We report this rare case with primary gastric ATLL and reviewing 13 cases previously reported.