Malignant neoplasias are the leading cause of death in Japan at present, of which hepatocellular carcinoma (HCC) ranks the third most frequent in men and the fourth most frequent in women. Annual deaths due to HCC are rising sharply and amounted to 33,000 in 1999. Chronic hepatitis C is the most frequent etiology of HCC in Japan and accounts for nearly 90% of cases. The recent rapid increase of HCC in Japan is a long-term sequel of hepatitis C virus infection that affected many individuals in the past, and manifests itself currently as HCC. Infection with the hepatitis C virus has prevailed since the end of World War II for reasons inherent in the socioeconomic background in Japan.