Changes in anal canal sensation after childbirth. Obstetic trauma predisposes to faecal incontinence. Anal canal sensation is impaired in incontinent patients. To assess the effect of childbirth on anal canal sensation anal mucosal electrosensitivity was measured in 122 primiparous patients in the immediate postnatal period and in 74 at 6 months postpartum. There were 35 normal vaginal deliveries, 36 forceps deliveries, 20 ventouse extractions, ten vaginal breech deliveries and 21 caesarean sections. Sensation was impaired in the lower, mid and upper anal canal immediately after delivery in those patients who had a normal vaginal delivery or a forceps delivery when compared with controls or with those delivered by caesarean section. Women who had ventouse deliveries had impaired sensation immediately after delivery in the mid anal canal compared with controls and those undergoing caesarean section. By 6 months there were no differences between any group. Patients who sustained a division of the external anal sphincter at delivery had impaired sensation which persisted in the upper anal canal at 6 months. 