Changes in hepatic fibrosis after interferon-based therapy may be important in determining the long-term outcome of chronic hepatitis C (CHC). The use of liver biopsy for posttreatment assessment is not a viable option as a routine follow-up procedure. This study evaluated the predictive value of a simple noninvasive index, the aspartate aminotransferase (AST)-to-platelet ratio index assessed 6 months after end of treatment (APRI-M6). We evaluated APRI-M6, platelet-M6, AST-M6, and alpha-fetoprotein-M6 of 776 CHC patients with interferon-based therapy as well as the parameters at baseline of 562 untreated patients who were evaluated to predict the risk of hepatocellular carcinoma (HCC) and mortality, during a mean follow-up period of 4.75 (1.0-12.2) and 5.15 (1.0-16) years, respectively. Based on analysis of receiver operating characteristics (ROC) and using optimized cutoff point, the APRI-M6 and platelet-M6 had superior prediction models for long-term outcome with area under the curve of 0.870-0.875 and 0.824-0.847, respectively, and accuracy of 78%-81% and 76%-78%, respectively, for interferon-based-treated patients. The predictive values of all 4 parameters were poor in untreated patients. In subgroup analysis, the APRI-M6 provided a more consistent prediction ratio than platelet-M6 for sustained responders and cirrhosis-free subgroups; both parameters had similar prediction power for nonresponders and were unsatisfactory in patients with cirrhosis. According to Cox proportional hazards analysis, cirrhosis and APRI-M6 were the 2 most important factors for predicting HCC. In conclusion, APRI-M6 can accurately predict the long-term outcome of patients subjected to interferon-based treatment. Nevertheless, the data needs further validation, particularly since the predictive accuracy for patients with cirrhosis is low.