OBJECTIVE: To obtain the following data that pertain to programs for the prevention of sexual abuse and sexual transmission of human immunodeficiency virus (HIV) to children: (1) to determine the prevalence of sexual abuse among siblings and other children cohabiting with sexually abused HIV-positive children, and (2) to determine if programs designed to restrain identified perpetrators from further acts of child sexual abuse were instituted. DESIGN: Case series. SETTING: Households of previously described sexually abused HIV-infected children. PATIENTS AND OTHER PARTICIPANTS: Twenty-two siblings or other children who lived in the homes of 14 previously described HIV-infected sexually abused children. Eight perpetrators of the abuse were identified. MAIN OUTCOME MEASURES: Sexual abuse of cohabiting children was confirmed with disclosure interviews, witness by other persons, diagnosis of another sexually transmitted disease, or an abnormal physical examination result that was highly suggestive of sexual abuse. Telephone contact with the Department of Social Services, county sheriff or police, and district attorney provided data regarding reports, criminal indictments, trials, convictions, and plea-bargain arrangements for the identified perpetrators. RESULTS: Eleven (50%) of the 22 cohabiting children were confirmed to have been sexually abused and four (18%) were suspected of having been sexually abused. Seven (32%) of the cohabiting children could not be examined and it was not known if they had been sexually abused. No assailant was tried for a criminal offense, required to participate in offender therapy, or prohibited from unsupervised visitation of children. CONCLUSION: Programs for the prevention of sexual abuse and sexual transmission of HIV to children require means of ensuring the safety of children exposed to perpetrators and require adequate supervision of perpetrators and their adherence to therapy.