During the period June 1989 to March 1991, laboratory evidence of sexually transmitted diseases (STD's) was found in 107 patients at the Red Cross War Memorial Children's Hospital in Cape Town, South Africa. Data were available on 96 patients aged 23 months to 14 years. Vaginal discharge was the most frequent presenting symptom (76 percent), particularly in those less than 5 years old (90 percent). Although a history of abuse was not given on presentation in 62 percent of the cases, evidence of abuse was subsequently elicited in 67 percent of patients. Neisseria gonorrhoea was the most common sexual pathogen (61 isolates, 8 penicillin resistant), followed by G vaginalis (17 isolates), Trichomonas vaginalis (7 infections), and T pallidum. Chlamydia trachomatis was shown by immunofluorescence in 14 children. Multiple STD's were found in 10 patients. Although evidence of childhood sexual abuse was not found in all patients with STD's, it was likely that the vast majority of patients had acquired these infections through sexual abuse. Symptomatic prepubertal children with G vaginalis isolates should be investigated for sexual abuse. Chlamydial immunofluorescence tests did not assist the diagnosis of sexual abuse in children and should, therefore, not be used, since they have no medicolegal significance. 5 tables and 18 references