OBJECTIVE: To explore the relative contribution of secular trends and public health policies to changes in sexual behaviour. DESIGN: Three random probability surveys of the sexual behaviour of people aged 18-69 years were conducted in 1970, 1992 and 2006 in France. METHODS: Data of the 2006 survey (n = 12,364) were compared with those from two surveys carried out in 1970 (n = 2625) and 1992 (n = 20,055). RESULTS: Over the last decades, median age at first intercourse has decreased by 4 years for women (22.0 in the 1930s vs. 17.6 in the 2000s) and 1 year for men (18.1 vs. 17.2). Lifetime number of sexual partners increased for women (1.8 in 1970 vs. 4.4 in 2006), but not for men (11.8 vs. 11.6). At the same time, the proportion of respondents, especially women, who reported nonpenetrative sexual practices and considered sexual intercourse essential to well being was on the increase. These changes are mainly attributed to an increase in women's social status. A marked increase in condom use was observed following the first AIDS/HIV prevention campaigns in the 1980s. CONCLUSION: Public health interventions that are synergistic with trends in social norms are likely to be more effective than those that run counter to them. In France, sexual health and HIV prevention policies aimed at harm limitation appear to have chimed with secular trends. The evidence of greater diversification of sexual practices offers potential to increase the range of safer sex messages used in public health interventions.