Objective: Many studies of sexual behaviour and condom use are based on data collected from university students. The aim of this paper is to determine whether first-year university students and their same-age peers have different patterns of sexual behaviour. Methods: Computer-assisted telephone interviews were completed by a representative sample of 19,307 Australian men and women aged 16-59 years (response rate 73.1%), 920 of whom were aged 17-19 years. Comparisons were made between reports of sexual risk behaviours from first-year university students and reports of the same behaviours from their same-age peers. Results: For female respondents, there were few differences in the sexual behaviour of first-year university students and their same-aged peers. For male respondents, there were some significant differences in the sexual behaviour of first-year university students and their same-aged peers and also different patterns of correlation between measures of sexual behaviour. Socio-demographic characteristics were related to whether 17-19 year-old respondents were first-year university students or engaged in other activities. Conclusions: The findings of studies of the sexual behaviour of university undergraduates should only be generalised to other groups with caution. The socio-demographic characteristics of the student population of a particular institution must be taken into account before generalisation to the broader population can safely be made from studies of single universities