Vertical transmission rates in Europe have decreased with the recent widespread introduction of interventions such as anti-retroviral therapy, elective caesarean section delivery and no breastfeeding. However, these interventions and changes tithe management of adult disease raise new and complex questions. The European Collaborative Study is a prospective cohort study of children born to HIV-infected women, set up in 1987 to clarify issues relating to HIV infection in pregnancy and childhood. To date 2600 mother-child pairs have been enrolled from 22 centres in European countries. Continued enrolment and follow-up are proposed to explore these new questions, including the issue of adverse effects resulting from exposure to prophylactic antiretroviral drugs, the impact of such exposure on timing of diagnosis and natural history of infected children and the quality of life of affected families, and continued monitoring of vertical transmission rates