There is a growing number of infected women in Europe and an increasing proportion of these have acquired their infection through heterosexual contact. Most infected women are of childbearing age and thus increasing numbers of children are at risk of acquiring infection. In this paper we examine the socio-demographic characteristics and trends in mode of acquisition of infection of 1690 infected women from 7 countries enrolled in the European Collaborative Study, a prospective multi-centre study of children born to women known to be HIV infected at or before the time of delivery. The majority of women were white, primiparae, married or cohabiting and born in Europe. Two-thirds had a history of injecting drug use (IDU), most commonly involving heroin. Although patterns of transmission varied by centre, there was a relative increase in heterosexual transmission over the study period. A history of needle-sharing among IDUs was common, but needle-sharing during pregnancy significantly declined between 1987 and 1994.