Objectives To determine to what degree the predominance of risky sexual behaviour during adolescence is the result of social influence, in particular that of peers, according to the perception of their attitudes and sexual behaviour. Methods Data were collected through structured and confidential individual interviews with 100 adolescents, selected randomly from among 1467 students attending one French high school. Results Although this study is of an exploratory nature, it reveals that the perception of peers is associated with a higher frequency of sexual initiation and commitment, including oral sex, but also commitment to protected sex. Sexual permissiveness of peers is associated with a higher frequency of sexual practices considered risky. The attitudes of peers with regard to contraception are associated with protective contraceptive attitudes, without a direct influence on behavioural patterns. Conclusions The sexual norms of peers influence youths' individual attitudes and behaviours. Gender differences in sexual socialization also play a role. Both aspects must be taken into account when devising prevention programmes concerning adolescent sexuality.