To determine the rate of mother-to-child transmission of hepatitis C virus (HCV) and identify risk factors associated with HCV transmission we prospectively studied 86 infants born to anti-HCV positive mothers. HCV infection was verified in all mothers before delivery and their HCV viral load was measured at or near delivery using reverse transcription polymerase reaction. For HCV genotyping the INNO-LiPA II probe assay was used. All mothers were tested for HIV infection. Possible risk factors for vertical transmission were recorded. The children were followed up for a minimum of 18 months for evidence of HCV infection, as determined by persistent HCV antibodies, or detection of HCV-RNA. Vertical transmission was restricted to infants born to viraemic mothers and the rate was 3.6% (95% CI 0.004-0.123). The HIV-infected mothers and those using drugs intravenously were more likely to transmit HCV to their children. The infected children had the same genotype as their mothers. Although the HCV RNA titre was higher in mothers who transmitted the virus than in those who did not, the viral load had borderline significance (p=0.08). Viral transmission was not influenced by mother's age, mode of delivery, genotype or type of feeding. Mother-to-child transmission of hepatitis C virus is uncommon and restricted to infants born to HCV viraemic mothers. Active drug use and HIV coinfection increase the risk for HCV vertical transmission.