A mass screening in 1990 of H town in Japan demonstrated a high prevalence of hepatitis C virus (HCV) infection in our previous studies. The purpose of the present study was to evaluate the prognosis and natural history of liver disease among the same residents after 12 years. Of 509 residents, 69 people had died, and 55 people had moved to other regions. In all, 139 persons of the remaining 385 residing in H town were examined for liver function tests, antibodies to HCV (anti-HCV), serum HCV RNA, and hepatitis B virus surface antigen (HBsAg). The data of 14 of these 385 people were collected from medical records. The cause of death of the 69 individuals was investigated. The prognosis of liver disease could be clarified after 12 years in 222 of the 509 residents. Most of the residents with liver disease had an advanced stage of disease. Of the 69 persons who died, the mortality rate caused by liver cirrhosis or hepatocellular carcinoma (HCC) was 44 and 53%, respectively, among 25 persons with positive anti-HCV, and 19 with positive HCV RNA. One person with positive HBsAg died of HCC. Persons with chronic HCV or HBV infection had significantly higher mortality rates from liver cirrhosis and HCC than those without infection (P<0.00001). The present study suggests that early detection and treatment for HCC should be carried out as HCV carriers age. Furthermore, persistent HCV carriers should receive therapy for suppression of the development of HCC. The eradication of HCC should be considered a national goal.