The present authors conducted a study of the occurrence of victimization and the perpetration of sexual abuse among 43 in-patients with intellectual disability aged between 9 and 21 years who were admitted to a child and adolescent psychiatric in-patient department over a period of 5 years. A retrospective case-note review was employed that explored the nature and severity of abuse in relation to the age, gender and level of disability. The prevalence of abuse or abusive behaviour, i.e. 14% of 300 admissions, did not change over time. In 13 out of the 43 cases, the issue of sexual abuse was identified after admission. Victimization alone occurred in 21 cases, perpetration alone in six cases, and both victimization and perpetration in 16 cases. Fifty per cent of the victims had been abused by a member of their close or extended family. Most cases (62%) were adolescents. There was only one instance of a victim being abused by a female. However, there were five girls who were perpetrators, all of whom had previously been victims. By contrast, 11 out of the 17 male perpetrators had been victims. Despite difficulties of disclosure, it was possible to establish that severely disabled patients had suffered sexual abuse. The present data support theories which (1) recognize gender differences in sexual abuse patterns and (2) have a developmental perspective, incorporating the influence of adolescence.