Young people's sexual behaviour is influenced by their perceptions of peer norms. In this survey of 445 people aged 16 to 29 years, 69% of participants believed they had fewer lifetime sexual partners than average. The mean number of actual lifetime partners reported was 5.5 and the mean perceived 'average' partners for peers was 6.6 (P < 0.01). When broken down by age and sex, the discrepancy was only significant for females aged 16 to 19. Comparison to a national survey also showed that peers' average sexual experience was overestimated. Adolescents are highly susceptible to the influence of peer norms, hence it is concerning that their perceptions of these norms are so distorted.