After hepatitis G virus (HGV) and GB virus type C (GBV-C) were independently discovered, it was determined that they were two isolates of the same virus. The HGV/GBV-C genome sequence and organization are closely related to hepatitis C virus. Although HGV/GBV-C infection is common and frequently persists in humans, infection has not been found to be associated with any known disease state. Because this virus is not associated with acute or chronic hepatitis, most people refer to it as GBV-C. GBV-C appears to grow in lymphocytes and not in hepatocytes, and presumably this is why the virus does not cause liver disease. Recent studies suggest that GBV-C infection in HIV-positive people is associated with prolonged survival. In vitro coinfection of human lymphocytes with GBV-C and HIV lead to decreased HIV replication. Further understanding of the mechanism(s) responsible for this interaction with HIV may provide novel approaches for treating HIV and AIDS.