Mother-to-infant transmission is the route by which the vast majority of children acquire HIV. Several refinements in our understanding in how to reduce the risk of transmission have been made in the past year. The risks from prolonged breast feeding, and the protective effects of caesarean section have been clarified. Shorter interventions using antiretroviral drugs are useful in resource-constrained settings. In developed countries, combination antiretroviral therapies to reduce maternal viral loads to below limits of detection are being explored, but there is concern about toxicity particularly of indinavir in pregnancy. Combining interventions can reduce transmission rates to less than 2%.