Data were collected from children with severe chronic constipation, and the appearance of the anus at presentation was noted. A visibly relaxed sphincter (indicating a degree of reflex anal dilatation) was seen in 20 children out of the 129 in whom this sign was sought. The only differentiating characteristic in this group of children was the greater degree of faecal loading judged on palpation of the abdomen. This evidence supports the hypothesis that constipation of such severity that it was referred to a specialised clinic can produce signs that may lead to an erroneous diagnosis of sexual abuse by anal penetration.