A 12-year-old boy with Down's syndrome presented with fever, arthritis and petechiae. Investigations revealed the presence of disseminated gonorrhoea. The patient made a good recovery after antibiotic therapy. A contact investigation was carried out, as well as talks with the family and school, and the case was reported to the Child Abuse Advice and Report Centre. The gonorrhoea was found to be caused by incest. Sexual abuse should be suspected in every child (certainly over the age of 1 year) with a sexually transmitted disease.