Background: Every year approximately 1500 adolescents (aged 12-20) are placed at Swedish detention homes run by the National Board of Institutional Care (SiS) according to the laws of “The young persons act” or “Secure institutional treatment for young offenders instead of prison”. Little is known about the sexual health of these adolescents, although earlier research, mainly international, strongly indicates that troubled youths in general are subjected to sexual exposure. Methods: A survey covering different aspects of sexual health with 148 boys (64 %) and girls (36 %) with an average age of 17 at Swedish detention homes was conducted. The survey focused sexual knowledge, attitudes and behaviours and the results were compared with the answers from other youths. Results: The adolescents at detention homes holds different attitudes towards sexuality compared to the ones in the national sample. They are to a greater extent, the boys more than the girls, negative towards homosexual relations; the girls’ sexual actions are judged harder than boys’; and none considered themselves as being homosexual although close to one third of the girls consider themselves as being bisexual. The average age for sexual debut, which most commonly took place with an older person with whom the boy or girl did not have an ongoing relationship, is three years earlier compared to other youths. Alcohol and drugs during sexual debut, experiences of sex against ones will, of selling and buying sex, of unprotected vaginal intercourse, of becoming or making someone pregnant is more common within the group. Conclusion: The results, although not unexpected, provides important knowledge to be used in comprehensive sexual health education which we suggest should be offered these young persons during their stay at the youth detention homes. The aim is to develop such a curriculum, let the detained adolescents reflect upon it in focus-groups and implement it.