BACKGROUND/AIMS: The purpose of this study is to elucidate the efficacy and safety of combined peginterferon and ribavirin therapy in Korean patients with chronic HCV infection. METHODS: We retrospectively analyzed the clinical records of 84 patients. Thirty five patients with genotype 1 HCV infection were treated with peginterferon alpha-2a 180 microgram/week and ribavirin 1,000-1,200 mg/day for 48 weeks, and 49 patients with genotype non-1 were treated with peginterferon alpha-2a 180 microgram/week and ribavirin 800 mg/day for 24 weeks. RESULTS: An early virologic response was seen in 87.0% of patients with genotype 1 HCV. An end of treatment response (ETR) was seen in 82.6% and 97.6% of patients with genotype 1 and genotype non-1, respectively. An overall sustained virologic response (SVR) was seen in 53 patients (82.8%) of the 64 patients: in 16 (69.6%) of 23 patients with genotype 1 and in 37 (90.2%) of 41 patients with genotype non-1. An end of treatment biochemical response was seen in 58 patients (90.6%) [genotype 1, 20 patients (87.0%); genotype non-1, 38 patients (92.7%)], and a sustained biochemical response was achieved in 49 patients (76.6%) [genotype 1, 14 patients (60.9%); genotype non-1, 35 patients (85.4%)]. Independent factors affecting an SVR were HCV genotype and the baseline HCV RNA level. CONCLUSIONS: This study shows that a combination therapy of peginterferon and ribavirin is highly effective for chronic HCV infection, producing a high SVR and ETR.