GBV-C and hepatitis G virus (HGV) are both RNA viruses from the Flaviviridae family. Molecular characterization of these viruses has shown them to be virtually identical to each other (1,2). GBV-C was first isolated in 1995 from an archival blood sample obtained in the 1960s from a surgeon with acute non A-E hepatitis (3). GBV-C has a 29% amino acid sequence homology with Hepatitis C Virus (HCV), another flavivirus (4). However, GBV-C in contrast to HCV, is not hepatotropic as the virus neither replicates primarily in hepatocytes nor causes acute or chronic hepatitis. Indeed, GBV-C does not cause any specific disease nor does it represent a substantial health risk in humans. Nevertheless, GBV-C infection is relatively common with a 2% prevalence rate in healthy blood donors, the majority of whom clear the virus and develop antibodies to the envelope glycoprotein E2.