In Japan, the national screening for the hepatitis C virus (HCV) has been started for both the general population and the high-risk groups. Our cost-effectiveness analysis was based on the result of the screening program including 99,001 people among the general population and 42,538 people among the high risk group from 2003 to 2006. The screening was performed using the three steps of the semi-quantitative HCV antibody test, the HCV core antigen test and the HCV-PCR test. A Markov model for HCV infected patients was constructed to estimate the future clinical benefits and the lifetime cost and the cost-effectiveness analysis was performed considering the recent treatment with peginterferon plus ribatvirin. In the cost-effectiveness analysis, the cohort, in which the screening was implemented (= screening strategy), was compared with the similar cohort without the screening (= no-screening strategy) in both the general population and the high-risk group, stratified by age. The infection rates of the general population and the high-risk group were 0.36% and 0.81%, respectively. The incremental cost-effectiveness ratio (ICER), a measure of cost-effectiveness, of the general population and the high-risk group was calculated to be from 848 to 4,825 and - 749 to 2,297 $/life expectancy gained, respectively. The treatment effectiveness, transition probabilities and the infection rate varied in the one-way sensitivity analyses, but the superiority of the screening strategy regarding the cost-effectiveness was unchanged. In conclusion, the screening strategy in both the general population and the high-risk group therefore appears to be more cost-effective than a no-screening strategy. © 2008 Tohoku University Medical Press.