To investigate influence of HIV co-infection on HCV, we examined 58 Japanese hemophiliacs with chronic hepatitis C(CHC) including 25 patients co-infected with HIV. HCV RNA levels and liver function were not affected statistically by the presence of HIV. Further studies are necessary to evaluate the impact of HIV on the prognosis of CHC in hemophiliacs. We were the first to report a beneficial effect of GBV-C/HGV infection on the course of HIV disease and many studies were confirmed our results. Discussions of these important issues such as impact of HIV on GBV-C/HGV and HBV have been performed in this paper.