Background: This study examines gender differences (and similarities) in the context, meaning and effects of unwanted sexual behaviour in secondary schools. Purpose First, the study's purpose is exploration of variables that discriminate between girls' and boys' experiences of unwanted sexual behaviour. Secondly, the aim is to find empirical grounding for diversity in schools' interventions and policies. Sample: Respondents were 2808 adolescents (14 or 15 years of age) in secondary schools, randomly selected in two regions in The Netherlands. Of the 22 schools that participated in the project, 30% were Catholic, 25% Protestant, 11% interdenominational (several religions within one school) and 38% of the schools were public schools. School size varied. The majority of the students' parents were born in The Netherlands (86%), 14% were born in Morocco, Turkey and Surinam. Design and methods: Survey questionnaires were to be completed during class time. Non-response rate: 2%. Analysis: discriminant function analysis. Results Girls more often experienced unwanted sexual behaviour by school personnel than boys. Their experiences were more often non-verbal in nature, physical or a combination of different sorts of behaviour. Girls experienced unwanted sexual behaviour as more upsetting than boys and they also experienced more psychosomatic health problems. The typical form of boys' experiences of unwanted sexual behaviour was verbal harassment by peers. The behaviour was less upsetting to boys and they experienced less psychosomatic health problems than girls. Conclusions: This study was the first attempt to find out whether girls' and boys' scores on several variables form a different type of unwanted sexual behaviour. Two different types of unwanted sexual behaviour were found. Although the context (locations and the presence of others) was more or less the same for both sexes, the meaning and the effects of unwanted sexual behaviour were clearly different for girls and boys.