Objective. The cumulative dosage of ribavirin per kilogram of body-weight prevents relapse and thus is a significant predictor of sustained virological response (SVR). Comparison of peginterferon (peg-IFN) alfa-2b/ribavirin and peg-IFN alfa-2a/ribavirin shows that the rates of SVR are similar, but the rates of relapse are significantly lower under the peg-IFN alfa-2b regimen. Depending on the weight-based ribavirin dose, patients with >105 kg reach a maximum of 13.2 mg/kg body-weight ribavirin in the peg-IFN alfa-2b regimen as opposed to only 11.3 mg/kg in the peg-IFN alfa-2a regimen. The aim of these investigations was to determine relapse rates in a retrospective analysis of 98 patients chronically infected with hepatitis C virus (HCV) genotype (GT) 1 in relation to the weight-based ribavirin dose. Material and methods. All patients completed treatment with peg-IFN alfa-2a/ribavirin (1000 mg/d or 1200 mg/d for patients weighing <75 kg or ≥75 kg) for 48 weeks. Classification of a low ribavirin dose with <13.2 mg/kg body-weight was used. Patients with a ribavirin dose ≥13.2 mg/kg were compared with those with a dose <13.2 mg/kg. Results. Patients with a ribavirin dose ≥ 13.2 mg/kg (n=84) showed a relapse rate of 19.0% in contrast to 71.4% in patients with a ribavirin dose of <13.2 mg/kg (n=14) (p=0.0013). The SVR rate was significantly higher in the ≥13.2 mg/kg ribavirin dosed group (59.5% versus 28.6%). Conclusions. Weight-adapted ribavirin dosing in combination with peg-IFN alfa-2a to avoid giving low doses of ribavirin should be evaluated. This will minimize relapse, especially in HCV GT 1 patients.