BACKGROUND The purpose of the study was to analyze serologic and molecular markers of the GB virus type C/hepatitis G virus (GBV-C/HGV) infection in voluntary blood donors from Southeastern France. METHODS Sera were tested for the presence of GBV-C/HGV RNA by reverse transcriptase-polymerase chain reaction and that of antibodies to the GBV-C/HGV E2 (anti-E2) antigen by an enzyme-linked immunosorbent assay. A first cohort (1660 blood donors) was tested prospectively and a second cohort (238 samples with hepatitis markers) was tested retrospectively. Donors in the prospective study were questioned for possible risk factors of virus transmission. Amplification products were sequenced and subjected to phylogenetic analysis. RESULTS Approximately 2.6 percent of individuals accepted for blood donation and 15.4 percent with positive hepatitis C virus serologic tests carried GBV-C/HGV RNA. Anti-E2 was detected in these two populations in approximately 12 percent and 48 percent of donors, respectively. Moderate relative risks were found only in tattooed or pierced individuals (1.82) and health care workers (2.45). Almost all strains were located in the same phylogenetic branch as HGV Group 2. CONCLUSIONS Though a large proportion of the donors tested have been in contact with GBV-C/HGV, no elevated relative risk of infection was identified. The phylogenetic distribution of viral strains suggests that the infection is endemic in this population.