Hepatitis G virus (HGV) infection is more common than hepatitis C virus (HCV) infection and is frequently found in healthy individuals. Although parenteral spread of HGV is well recognized, other routes of transmission probably occur as well. In a prospective study of mother-to-infant transmission of hepatitis viruses, 69 pregnant women with antibodies to HCV and their 81 newborn children were included. Serum levels of HCV RNA and HGV RNA were detected by polymerase chain reaction (PCR) assays, and antibodies to HCV and HGV envelope protein E2 were detected by enzyme-linked immunosorbent assay. Fifty-nine of the mothers had HCV viremia, whereas 16 had HGV viremia. HCV transmission from viremic mothers occurred in 2.8%-4.2% of the cases, whereas HGV transmission from viremic mothers occurred in 75.0%-80.0% of the cases (P < .001). Sequencing of the PCR products of HGV from the mother-infant serum pairs showed minor differences in most cases but sequence homology in each pair. Although the rate of perinatal HGV transmission highly exceeded that of perinatal HCV transmission, HGV did not seem to induce hepatitis in the children.