Mortality rates from chronic liver diseases (CLD) such as liver cirrhosis and hepatocellular carcinoma have been reported to be higher in Tokushima prefecture, although its causes remain unclear. To clarify the causes of CLD in Tokushima prefecture, we evaluated the positive rates of HBs antigen and anti-HCV antibody and the mortality rates from CLD in patients with liver diseases and blood donors after dividing the entire Tokushima prefecture into 8 district boundaries of health centers. In addition, to evaluate the causes of the higher frequency of CLD and the relationship between the development of CLD and viruses, medical examinations were performed in 2 mountain villages in Tokushima prefecture where the drift of population was limited and the mortality rates from CLD differed from each other. As a result, it was found that HCV infection was the major cause of the higher mortality rates from CLD in Tokushima prefecture. Although there were marked regional differences in the mortality rates from CLD, they were mainly due to different rates of HCV infection.