Little is known about the molecular anomalies involved in the development and progression of malignancy of pancreatic endocrine tumors (PETs). A recently identified member of the Ras family, Ras homologue member I (ARHI), has been shown to be involved in breast, ovary, and thyroid carcinogenesis. Unlike other members, it acts as a tumor suppressor gene that inhibits cell growth. Here we analyzed the mRNA expression of ARHI in 52 primary PETs and 16 normal pancreata using quantitative reverse transcription-polymerase chain reaction. ARHI expression showed a statistically significant difference between either normal pancreas or well-differentiated endocrine tumors (WDET) and poorly differentiated endocrine carcinomas (PDECs) (P < .001 and P < .001, respectively). Moreover, ARHI expression among WDEC samples was more heterogeneous than in WDET, with several tumors showing level of expression analogous to that observed in PDECs. A significant correlation between lower ARHI expression and shorter survival (P = .020) was identified, and a low ARHI expression was associated to a shorter time to progression (P < .001), even considering the proliferation index Ki67 in the multivariate analysis. ARHI is involved in PET progression. Its mRNA expression seemed to be a prognostic factor for disease outcome and, in association with the proliferative index Ki67, a predictor for a rapid tumor relapse.