Sexual experiences of 1255 adolescents admitted to a juvenile detention facility were assessed through their responses to a health history questionnaire. More than 80% reported sexual experience. Age at first intercourse acknowledged by females was early (mean 13 years) but rarely prepubertal and was similar for blacks and non-blacks. Males commonly reported beginning sexual experience before age 10 years (40% in blacks and 20% in nonblacks). Sexual activity continued in most, with 73% of the sexually experienced teens reporting intercourse in the month prior to admission. Reports of recent sexual activity increased with age in all race/gender groups. For females, 26% reported sexual misuse compared to 2% of the males. Willingness to answer questions about sexual experiences varied with the question and increased with age. Prepubertal sexual activity is a more common phenomenon than is generally acknowledged. To what extent the experiences reported in our study represent the norm for behavior among individuals of similar back-ground requires further study.