Antepartum plasma hepatitis C virus (HCV) RNA was quantified in 155 mothers coinfected with HCV and human immunodeficiency virus type 1 (HIV-1), and HCV RNA was serially assessed in their infants. Of 155 singleton infants born to HCV antibody-positive mothers, 13 (8.4%) were HCV infected. The risk of HCV infection was 3.2-fold greater in HIV-1-infected infants compared with HIV-1-uninfected infants (17.1% of 41 vs. 5.4% of 112, P = .04). The median concentration of plasma HCV RNA was higher among the 13 mothers with HCV-infected infants (2.0 × 106 copies/mL) than among the 142 mothers with HCV-negative infants (3.5 × 105 copies/mL; P < .001), and there were no instances of HCV transmission from 40 mothers with HCV RNA concentrations of < 105 copies/mL. Women dually infected with HIV-1 and HCV but with little or no detectable HCV RNA should be reassured that the risk of perinatal transmission of HCV is exceedingly low.