PURPOSE: Recently, it has been reported that Epstein-Barr virus (EBV) is associated with some gastric cancers. But EBVs role in EBV-associated gastric carcinomas (EBVaGCs) has not been fully elucidated. This study was undertaken to evaluate the characteristics of EBVaGCs and to compare those with non-EBVaGCs. MATERIALS AND METHODS: EBV infection was studied using paraffin-embedded tissue blocks of 119 cases of gastric adenocarcinomas by in situ hybridization for EBV-encoded small RNAs (EBERs). In EBVaGCs and non-EBVaGCs, molecular characteristics were evaluated by immunohistochemical staining for latent membrane protein (LMP)-1, p53 protein, and proliferating cell nuclear antigen (PCNA). RESULTS: EBERs were detected in 12 cases (10.1%) of 119 gastric adenocarcinomas. LMP-1 was negative in all carcinomas tested, p53 protein was positive in 7 cases (58.3%) of 12 EBVaGCs and in 51 (47.7%) of 107 non-EBVaGCs, the difference between two groups being not significant. Mean PCNA index was 38.2+-26.1% in EBVaGCs and 22.8 +- 20.0% in non-EBVaGCs. The index was significantly higher in the former than in the latter. CONCLUSION: These results suggested that neoplastic progression in EBVaGCs was implicated with high expression of PCNA, but not consistently with overexpression of p53 protein or LMP-1.