Forty-four consecutive patients with incontinence of solid stool of traumatic or idiopathic aetiology were examined by anal endosonography and standard anorectal physiology tests. Anal endosonography showed an external anal sphincter defect in four out of 11 (36 per cent) patients with idiopathic (neurogenic) incontinence. In the remaining seven patients both parts of the sphincter were intact and a linear relationship was found between the resting anal canal pressure and the endosonographic thickness of the internal anal sphincter. Twenty-eight out of 33 (85 per cent) patients with incontinence of traumatic origin had external sphincter defects, confirmed by concentric needle electromyogram mapping in the 19 patients in whom this was performed. Eleven of these 28 (39 per cent) patients also had disruption of the internal sphincter. Anal endosonography has revealed significant abnormalities in patients with faecal incontinence and has a complementary role to anorectal physiology in the routine investigation of these patients.