Hepatitis C virus (HCV) infects an estimated 170 million persons worldwide, and 2 million persons in Japan. HCV is a major cause of chronic liver diseases, especially hepatocarcinogenesis, and the number of patients with HCV-related hepatocellular carcinoma (HCC) is increasing worldwide as well as in Japan. Most patients with acute hepatitis C develop chronic hepatitis. Spontaneous disappearance of HCV in patients with type C chronic liver disease is uncommon, and it tends to progress to further advanced and more severe liver disease, ultimately to HCC over a period of 30 years in most cases. Chronic liver disease due to HCV infection is commonly associated with extrahepatic manifestation, for example cryoglobulinemia. Antiviral treatment for HCV infection with interferon alone during 24 weeks was associated with a low rate (less than 10%) of sustained virologic response (SVR), especially in patients infected with HCV genotype 1b and high HCV RNA concentration. However, combination therapy of interferon and ribavirin raises the SVR rate. More recently, pegylated interferon used for treatment of chronic hepatitis C resulted in a high SVR rate. These modalities of antiviral treatment will reduce HCC occurrence. So far, there is no HCV vaccine in spite of many efforts.