OBJECTIVES: To estimate the proportion of individuals in the general population who did not notify their sexual partners at the time of an STD diagnosis, according to the sex of the patient and the type of partner.¦METHODS: We analysed behaviour at the time of diagnosis of a self reported STD, using data from three large French national population based surveys of adults (ACSF, Barométre Santé) and adolescents (ACSJ). Univariate and multivariate analyses took into account the complex sampling design.¦RESULTS: In the ACSF, 14% (95% CI: 4% to 24%) of men reported that they had not informed their main sexual partner compared with only 2% (95% CI: 0% to 5%) of women (p = 0.03). This sex difference was independent of the nature of the STD, the patient's age, level of education, and number of partners. Similarly, in the ACSJ, 51% (95% CI: 21% to 81%) of boys reported that they had not talked about this STD with their current sexual partner compared with only 9% (95% CI: 0% to 26%) of girls (p = 0.04). Notification by a sexual partner had led to discovery of the STD more frequently in male subjects than in female subjects, both in adults (32% of men compared with 4% of women (p=0.04)), and adolescents (36% of boys compared with 12% of girls). Most subjects, irrespective of sex, had not informed partners other than their main or current partner: 73% (95% CI: 62% to 84%) of adults and 86% (95% CI: 77% to 95%) of adolescents.¦CONCLUSIONS: Procedures must be developed urgently to improve the notification of sexual partners, particularly female partners and adolescents, who are unlikely to be tested early without such notification.