Forty-three primary gastrointestinal T cell lymphomas were investigated for the presence of Epstein-Barr virus (EBV) by polymerase chain reaction, RNA in situ hybridization, and immunohistochemistry. In addition, the association between EBV and clinicopathological characteristics of these lymphomas was investigated. Five of the thirty-eight cases that could be evaluated expressed EBV-encoded nonpolyadenylated RNA-1 in most tumor cells. Two of these five cases were EBV latent membrane protein-1 positive. All five cases were CD30 positive. In three of these five EBV-associated T cell lymphomas, the tumor cells were considered to be the neoplastic counterparts of activated cytotoxic T cells as shown by the expression of granzyme B. There was no association with histological characteristics of gluten-sensitive enteropathy, angioinvasion, necrosis, eosinophilia, or epitheliotropism of the tumor cells. The substantial percentage (58%) of EBV DNA polymerase chain reaction-positive cases was largely the result of the presence of EBV-encoded RNA-1-positive reactive cells. In conclusion, EBV might have an important etiological role in only 13% of the primary gastrointestinal T cell lymphomas. This percentage is similar to the findings in primary lymph node and lung T cell lymphomas.