Forty six patients (median age 61 years; 42 women) with faecal incontinence and 16 age and sex matched controls undergoing a restorative proctocolectomy were assessed by clinical examination, anorectal physiology, and anal endosonography. Forty patients (87%) with faecal incontinence had a sphincter defect demonstrated on anal endosonography (31 external and 21 internal anal sphincter defects). The commonest cause of faecal incontinence was obstetric trauma. This occurred in 35 women, 30 of whom exhibited a morphological defect in the anorectal sphincter complex. In 22 of these patients with a history of a perineal tear or episiotomy, 21 (95%) had a sphincter defect. Sphincter defects were commonly located at the level of the midanal canal.