It is difficult to achieve a sustained virologic response from antiviral therapy for genotype 1 hepatitis C virus-infected patients without a sufficient virologic response in the early weeks after treatment. However, a recent study has reported on the effectiveness of an extended course of treatment with peginterferon alpha-2a plus ribavirin for slow virologic responders. The aim of this study was to evaluate the economic impact of an extended course of treatment. A Markov cohort model of hepatitis C was designed in order to demonstrate the clinical states, based on the assigned transition probabilities over 30 years. The slow virologic responders treated with an extended 72-week course of therapy could increase by 0.55 the quality-adjusted life years (=15.35-14.80) and reduce the lifetime cost by $2762 (=71 559-69 438) in comparison with those treated by the standard 48-week course. One-way sensitivity analyses did not change the cost-effectiveness. Therefore, the extended 72 weeks of treatment with peginterferon alpha-2a plus ribavirin for slow virologic responders could be cost-effective in comparison with the standard 48 weeks of treatment.