In chronic hepatitis C (CHC), treatment duration may be individualized according to time to first undetectable hepatitis C virus (HCV) RNA, with patients who attain undetectable HCV RNA early in treatment being candidates for shorter regimens. The aim of this study was to determine the relapse rate in patients with CHC genotype (G) 1 infection and low baseline viral load who achieved undetectable HCV RNA by week 4 [rapid virologic response (RVR)] when treated for 24 weeks. This was an open-label, multicentre, noninterventional study. Adult patients with G1 CHC infection and baseline viral load <600,000 IU/mL who attained RVR were treated with peginterferon alfa-2b (1.5 μg/kg/week) plus ribavirin (800-1200 mg/day) for 24 weeks, then followed for a further 24 weeks. The primary endpoint was relapse rate, defined as the proportion of patients with undetectable HCV RNA at treatment week 24 and detectable HCV RNA at week 24 follow-up. The secondary efficacy endpoint was sustained virologic response (SVR). Overall, 170 patients were included in the efficacy-evaluable population. The relapse rate was 9.7% (16/165, 95% confidence interval: 0.06-0.15), and SVR was attained by 149 of 170 patients (87.6%). Virologic outcomes were consistent regardless of age, gender, body weight and genotype. Seven patients reported treatment-emergent serious adverse events (AEs), and four patients discontinued treatment because of an AE. This study further demonstrates that peginterferon alfa-2b plus weight-based ribavirin for 24 weeks is an effective treatment strategy for treatment-naive patients with G1 CHC and low viral load who attain RVR. © 2011 Blackwell Publishing Ltd.