In contrast with the psychologically based individualistic models of health behaviour in which conduct adopted in response to AIDS risk is seen as an individual decision depending on the processing of information, we postulate that individuals construct their own definition of the risk of HIV transmission by drawing on their socio-sexual lifecourse and the type of sexual relationships in which they are engaged. Data were obtained from a random sample of 4820 people living in France interviewed by telephone between September 1991 and February 1992. This analysis was conducted on a subgroup of 1508 men and 1376 women in sexual relationships of less than five years. Multiple correspondence analysis and logistic regression were performed. Our findings show that the adoption of preventive behaviour is far from depending exclusively on the awareness of risk. Individuals having a diversified sexual experience, who talked about sexuality during their childhood and have personal confidants more often reported having changed their sexual behaviour because of AIDS. Although less likely to select their partner in order to reduce the risk of AIDS, they more often adopt strategies directly linked to sexual interaction such as condom use. Individuals belonging to networks in which condom use is the norm are more likely to use them. Women, for whom stable relationships propitious to the development of emotional closeness carry a high social value, are more likely to rely on uniquely relational strategies in which the adaptation to the risk of infection involves a better knowledge of the partner. Our findings reveal that individuals attach a different degree of risk to their partners depending on whether they occupy a central or peripheral place in their network of sociability. Furthermore, we observed an incompatibility between the preventive and the socio-affective rationale in which condom use is inversely related to the degree of intimacy, regardless of what is known about the partner's serological status. Risk adaptation strategies are thus far from being irrational, but are related to individuals' socio-sexual biography, the logics of gender, social networks and milieux of sociability, and depend ultimately on the context of the relationship. As with other health-related behaviour, coping strategies appear to be the product of a complex interaction of biographical, social and cultural threads. Prevention campaigns based exclusively on the promotion of individual responsibility are thus likely to miss the mark. Copyright (C) 1997 Elsevier Science Ltd.