Anti-hepatitis C virus (HCV) antibody was measured by a second-generation EIA in the residents of two sanatoriums of leprosy (A, B) in Japan. The prevalence of anti-HCV antibody (HCV+) was 60.5% in sanatorium “A”, and at least 23.1% in sanatorium “B”. It was inferred that having past history of leprosy and institutionalized lifestyle for long period had some influence on the extraordinary high prevalence of HCV infection. The cases of LL and BL, classified by leprosy classification, had significantly higher prevalence of HCV + than the cases of other forms of leprosy. The HCV-carrier rates in HCV + were relatively low as of 44.9% (A: high antibody titer) and 48.4% (B: HCV-RNA positive) than that shown in previous studies. The risk of HCV infection in the married couples could not be considered high. Significantly more cases with low platelet count and the cases with liver dysfunction were found in HCV-carrier group than in non-carrier or HCV-group. In HCV-group, significantly more cases with low platelet count and the cases with high γ-GTP were found in male than in female. Although there was no significant difference in the results of urinalysis between the three groups such as HCV-carrier, non-carrier and HCV-, hematuria was more prevalent than proteinuria in all three groups. Hence the disease of leprosy than HCV infection might have affected the renal function more. The residents in sanatoriums should be followed-up considering HCV infection and the past history of leprosy.