OBJECTIVE: There is evidence to suggest that hepatitis C virus (HCV) infection is a high-risk condition for developing type 2 diabetes. However, there are no interventional studies that confirm that HCV infection causes diabetes. The main aim of this study was to compare the incidence of glucose abnormalities (diabetes plus impaired fasting glucose) between HCV-infected patients with or without sustained virological response (SVR) after antiviral therapy. RESEARCH DESIGN AND METHODS: Patients with normal fasting glucose (<100 mg/dl) with biopsy-proven chronic hepatitis C without cirrhosis and with at least 3 years of follow-up after finishing antiviral therapy were included in the study (n = 234). Patients received interferon alpha-2b (alone or with ribavirin) for 6 or 12 months according to genotype. Cumulative incidence of glucose abnormalities was evaluated by using the Kaplan-Meier method comparing subjects with and without a SVR to antiviral treatment. A multivariate Cox proportional hazards analysis was performed to explore the variables independently associated with the development of glucose abnormalities. RESULTS: During follow-up, 14 of 96 (14.6%) patients with SVR and 47 of 138 (34.1%) nonsustained responders developed glucose abnormalities (P = 0.001). Patients with SVR did not develop diabetes during follow-up, whereas nine cases of diabetes were detected in nonsustained responders (P = 0.007). After adjustment for the recognized predictors of type 2 diabetes, the hazard ratio for glucose abnormalities in patients with SVR was 0.48 (95% CI [0.24-0.98], P = 0.04). CONCLUSIONS: Our results provide evidence that eradication of HCV infection significantly reduces the incidence of glucose abnormalities in chronic hepatitis C patients. In addition, this study supports the concept that HCV infection causes type 2 diabetes.