The aim of this research was to explore unwanted sexual behaviour amongst young people. Sexual aggression was operationalized at three levels: "verbal", "non-verbal/intimidating" and "physically violent". A total of 1,700 Dutch adolescents completed a questionnaire that included six clusters of possible determinants of unwanted sexual behaviour: background characteristics, personality characteristics, family environment, school environment, friends and deviant behaviour and sexuality and relationships. We found that victims of unwanted sexual behaviour are often perpetrators, and perpetrators are often victims. The adolescent phase can be a time of sexual exploration for many young people when they explore their own boundaries and those of others. In so doing they run the risk of transgressing boundaries and thereby becoming a victim or perpetrator of unwanted sexual behaviour. (Contains 1 table and 1 figure.)