Globally the HIV epidemic mainly affects young people, particularly young females who are vulnerable to acquisition of HIV as a result of their biological and social susceptibility. Women represent an increasing proportion of newly diagnosed HIV cases in Western and Eastern Europe, reaching 35% and 40%, respectively, in 2004. In the European Collaborative Study (ECS), HIV-infected pregnant women are enrolled and their infants followed-up prospectively. By the end of 2005, 5956 women had enrolled, of whom 1912 (32%) were aged?