Although 5-10% of gastric carcinoma (GC) cases worldwide are associated with EBV, a human herpesvirus, it is still not clear what the precise contribution of the virus is to the pathogenesis of EBV-positive GC. Here we report that EBV infection induces expression of insulin-like growth factor 1 (IGF-I) in the GC-derived EBV-negative cell line NU-GC-3 and that the secreted IGF-I acts as an autocrine growth factor. Transfection of individual EBV latent genes into NU-GC-3 cells revealed that the EBV-encoded small RNA (EBER) was responsible for IGF-I expression. Addition of recombinant IGF-I accelerated growth of NU-GC-3 cells, whereas growth of the EBV-converted NU-GC-3 cells was blocked by treatment with an anti-IGF-I antibody. These results suggest that IGF-I induced by EBER acts as an autocrine growth factor for EBV-positive GC. These findings seem to be operative in vivo, as EBV-positive GC biopsies consistently express IGF-I, whereas EBV-negative GC biopsies do not. EBER is invariably expressed in EBV-associated malignancies including GC. The present findings strongly suggest that EBV directly affects the pathogenesis of EBV-positive GC and underline the importance of RNA molecules on cell growth regulation.