This study confirms the observation that some gastric adenocarcinomas contain Epstein-Barr viral (EBV) sequences in their carcinoma cells. EBV sequences were detected by polymerase chain reaction and in situ hybridization in the tumors of 19 of 187 (10.2%) Japanese-American men and women living in Hawaii. The EBV-associated gastric cancers were more frequently present in men than in women: 14 of 99 (14.3%) men versus 5 of 88 (5.7%) women (P = 0.046). EBV type A was found in 17 of the 19 EBV-associated cancers, a finding consistent with the type A predominance in Japanese populations. Intestinal and diffuse-type tumors were both EBV-positive, and moderate to marked inflammation was usually present. The virus was not found in adjacent normal nonneoplastic mucosal cells or in mucosa showing intestinal metaplasia. EBV-associated tumors were found at stages 1 or 2 in 53% of cases, compared with 36% of the EBV-negative cancers (P = 0.13). The presence of EBV did not appear to influence survival. The relatively high incidence of gastric cancer compared to other EBV-associated tumors makes EBV-associated gastric cancer potentially one of the most common EBV-related tumors in the United States.