Like many other countries in South East Asia, Cambodia is experiencing a rapidly developing AIDS epidemic. Groups reported as being particularly seriously affected include sex workers and their clients. Young people too may be at heightened risk: some young women find sex work a lucrative option in the context of low wages and poor employment opportunities, and some young men pay for sex either as individuals or as part of group socializing. These same young men may subsequently have sex with other partners, thus extending networks of transmission. While there is limited knowledge about the form of such sexual networks, little is known about the meanings that underpin young people's sexual relations and partnerships, the sexual identities associated with such meanings, and prevailing socio-sexual cultures. This paper reports on findings from an in-depth qualitative study conducted among two groups of young people: one urban, the other rural. Following an initial Rapid Assessment Process, data was collected via individual interviews, focus group interviews and participant observation. The research team included young people themselves. Data is presented on dominant discourses about sex and sexuality in Cambodia; contemporary patterns of sexual behaviour; sexual meanings and sexual practices; sexual relations among young people involving payment; and sexual relations not involving payment. The implications for more effective HIV prevention efforts are discussed.