In Africa, where HIV/AIDS is widespread and HIV is mainly spread by heterosexual intercourse and from mother to child during pregnancy, childbirth or breastfeeding, the couple is the primary site of sexual HIV transmission. When a woman is infected with HIV, the decision to have a child involves the risk of vertical transmission. This article, based on a review of African studies of the subject and results of research programmes conducted in Abidjan between 1997 and 2001, examines changes in sexual and reproductive behaviour in the face of the AIDS threat. After a preliminary overview of trends in the general population, the article focuses on women who have learned during pregnancy that they are HIV-positive, through a mother-to-baby HIV-transmission prevention programme. It discusses how they manage the risk of sexual and vertical transmission of the virus, in their couple and their reproductive decisions. The difficulty these women have in divulging their HIV infection to their partners and then negotiating the adoption of new practices proves to be a major obstacle to behavioural change. The success of future prevention programmes will depend on their ability to take the relationship between man and woman in the couple into account.