We conducted a case-control study to elucidate factors contributing to the development of hepatocellular carcinoma (HCC) in Hyogo Prefecture, Japan where its incidence is high. In this study, the incidence of hepatitis virus infection in HCC patients and lifestyle factors including dietary and drinking habits were investigated. One hundred and eight patients with HCC (89 males and 19 females) and 93 controls (63 males and 30 females) were enrolled. Hepatitis C virus (HCV) antibody was identified in 87% of cases of which HCV-RNA was further detected in more than 95%. Genotype distribution of HCV was similar to that reported for the Japanese infected with HCV. There was a positive correlation between HCC and history of blood transfusion (both male and female) and surgery (male). Alcohol consumption over a period of 30 years was higher in the HCC patients than in controls; but not significant. These data indicated that HCV infection is a primary contributing factor to the development of HCC in Hyogo Prefecture.