Objective: The objective of the study was to determine the prevalence of sexual abuse in female adolescents in Istanbul, Turkey from data collected as part of a school-based population study on health and health behaviors. Method: A stratified cluster sampling procedure was used for this cross-sectional study. The study sample included 1,955 randomly selected 9th through 11th grade female students attending 26 randomly-selected high schools in Istanbul. A self-report questionnaire was administered anonymously in the classroom. Information on sexual abuse history was collected through the questions investigating ''touching'' and ''intercourse.'' Results: Of 1,955 female students, 1,871 (95.7%) provided answers to the questions addressing unwanted sexual experience. Of these, 250 (13.4%) reported sexually abusive experiences. Two hundred and thirteen (11.3%) students reported that someone touched their private parts in a way they did not like; 91 (4.9%) reported they were forced to have sexual intercourse; 54 (3.0%) reported both types of sexual abuse. Incest was reported by 1.8% of the subjects. Ninety-three percent of the perpetrators were reported to be male. Conclusions: This is the first reported school-based study to determine the prevalence of sexual abuse in Turkey. The results show that at least 13.4% of female high school students disclosed having experienced sexual abuse during childhood.