OBJECTIVES: The cost-effectiveness of peginterferon and ribavirin (PEG_IFN+RBV) for elderly patients with chronic hepatitis C (CHC) was investigated. A nationwide registration of interferon-treated hepatitis patients has been conducted in Japan since 2009. This study was based on individual patient data from the registration for investigation in a real-world setting.  METHODS: PEG_IFN+RBV-treated CHC patients 65-years or older were analyzed. All registered patients received antiviral treatment, and were assumed to suffer if not treated. The incremental cost and effectiveness of treatment was estimated as the difference between actual events and the assumed longstanding disease status. The individual patient data regarding age, gender, and duration of and response to treatment was used to estimate cost of PEG_IFN+RBV, cost of following CHC, and quality-adjusted life-year (QALY). Incremental cost effectiveness ratio (ICER) and 95% bootstrap confidence interval (CI) were calculated, and probabilistic sensitivity analysis (PSA) was done for assumptions on the distribution of uncertain data. Conservative assumptions were used throughout the analysis.  RESULTS: There were a total of 1378 patients (median age 68 y; range 65 – 80 y). 1005 patients had hepatitis C virus type 1 (72.9%), and 1269 had a high viral load (92.1%). A platelet count of <100,000/mm3 was found in 152 patients (11.0%), 100,000 – 150,000/mm3 in 541 patients (39.3%), and ³150,000/mm3 in 655 patients (47.5%). 1106 patients completed the planned treatment (80.3%). Sustained viral response was observed in 650 cases (47.2%), relapse in 404 cases (29.3%), and no response in 324 cases (23.5%). Incremental cost was calculated to be 1.885 million yen (approximately 16,390 euros) for a patient, and effectiveness was 0.657 QALY. ICER was 2.869 million yen (approximately 24,950 euros)/QALY (95% CI: 2.665 – 3.089 million yen /QALY). PSA showed that most trials had ICER of less than 4.00 million yen/QALY.  CONCLUSIONS: The ICER of PEG_IFN+RBV for elderly patients with CHC seemed acceptable.