Assessment of the efficacy of a prevention of mother-to-child transmission (PMTCT) programme in a routine service setting in comparison to a research environment.Descriptive study over a 13-month period utilising retrospective data obtained from hospital records complemented by prospective data on a sample of patients enrolled in a study to determine an affordable HIV diagnostic protocol for infants.Routine PMTCT service at Coronation Women and Children's Hospital (CWCH) situated in Johannesburg and affiliated to the University of the Witwatersrand.Pregnant women known to be HIV infected who delivered at CWCH from 1 October 2001 to 31 October 2002.The HIV transmission rate to infants, which reflects nevirapine (NVP) delivery and infant feeding practices, and follow-up rates of perinatally exposed children.Of the 8,221 deliveries, 1,234 (15%) occurred in women known to be HIV infected. HIV transmission rates of 8.7% at 6 weeks and 8.9% at 3 months of age in the study population verifies the high rate of NVP administration and the ability of women to formula-feed their babies and abstain from breast-feeding. More than one-third of infants never return for follow-up and more than 70% are lost to follow-up by 4 months of age.The low HIV transmission rate confirms the efficacy of this routine service PMTCT programme. HIV-infected children are not being identified for medical management as part of PMTCT follow-up. It is imperative that record keeping is improved to facilitate ongoing monitoring.