Recently, one of non-A to E hepatitis viruses was identified and the new virus was named HGV/GBV-C(HGBV-C). In Japan, more than 90% of liver cirrhosis and hepatocellular carcinoma were associated with hepatitis B or C virus infection. Proportion of HGBV-C infection was only 3.4% of patients with non-A to E chronic liver disease we examined. Thus, HGBV-C was considered to play only a minor role in chronic liver disease of unknown etiology. HGBV-C positive cases have a history of blood transfusion and/or operation and/or drug self-injection, and frequently co-infected with hepatitis C virus. Whether HGBV-C infection really causes severe chronic liver disease is required to be elucidated.