Thirty-eight women with rupture of the anal sphincter occurring during childbirth were followed for 3-12 months. Nineteen had complete rupture of the external anal sphincter, 14 had a lesion involving more than half of the sphincter muscle and five had a superficial rupture. Fourteen patients presented with continence disturbances: nine to solid or liquid faeces and five to flatus. Incontinence was present in nine women 3 months after childbirth. Anal manometry and electromyography were performed in patients 3-5 days after delivery and repeated at 3, 6 and 12 months. Manometry and electromyography were also performed in 16 control subjects who were nulliparous or had given birth more than 2 years previously and 24 primiparous controls, who were investigated at 3-5 days and at 3 months. There were significant differences between both incontinent and continent patients compared with nulliparous and primiparous controls. Primiparous control subjects had decreased anal squeeze pressure as well as decreased electromyographic activity on the first days after delivery compared with nulliparous controls. After 3 months no differences were found. Continence disturbances are frequent after sphincter rupture; these patients should be monitored after delivery and those with persisting incontinence offered sphincter repair.