The association of Epstein-Barr virus (EBV) with lymphoepithelioma-like carcinoma in the nasopharynx, which is common in Chinese from the southern region, is well established. Recently, EBV has also been found to be associated with lymphoepithelioma-like carcinomas (LELCs) and carcinomas with prominent lymphoid infiltrates in the stomach. We investigated for the presence of EBV in 74 cases of gastric adenocarcinoma and 36 cases of colorectal adenocarcinoma from Chinese patients by in situ hybridization (ISH) using an antisense EBER probe. In seven cases (9.5%) of gastric carcinoma, EBER was highly expressed in the adenocarcinoma cells and metastatic tumor cells in regional lymph nodes. In all these cases, the normal gastric epithelium was EBV negative. None of the colorectal carcinomas showed a positive signal. Isolated positive lymphoid cells were frequently found in both tumors. Of the seven positive cases, only one was LELC, and the others were conventional adenocarcinomas of the intestinal type. Five showed expression of the viral RNA in all tumor cells as well as the surrounding dysplastic epithelium. Interestingly, the sixth case showed distinct negative islands of dysplastic glands adjacent to strongly positive dysplastic glands and invasive carcinoma cells. This pattern of positivity, together with negative normal gastric epithelium and positive metastatic tumor, suggested that EBV infection occurred in the dysplastic phase and that an apparent growth advantage was conferred by the EBV infection.