BACKGROUND Rupture of the anal sphincters at childbirth is considered rare in obstetric literature. Long-term effects are sparingly mentioned. In clinical practice, however, it is not uncommon to meet women with anal incontinence. The aim of our study was to record the incidence and to evaluate the consequences of rupture of the anal sphincter at childbirth. METHODS Fifty-one consecutive women with primarily sutured anal sphincter rupture and 31 women without anal sphincter rupture were prospectively studied after vaginal delivery. All were assessed clinically at 3 days, 6 weeks, and 6 months after delivery. After 6 months, all women underwent anorectal manometry and answered a questionnaire about incontinence, social function, and general health. RESULTS The overall incidence of sphincter rupture was 2.4 percent. Significantly lower values were found for maximum anal squeeze pressure and squeeze pressure area 6 months postpartum in the women with sphincter rupture compared with those without rupture. The resting pressures did not differ between groups. Approximately 40 percent of the women in both groups had noted some fecal incontinence by 6 months postpartum. Symptoms were significantly more severe in patients with sphincter rupture. CONCLUSIONS Anal sphincter rupture was 2.4 times as common as reported in Swedish birth statistics. The high incidence of fecal incontinence by 6 months postpartum in all women is surprising and deserves further investigation, specifically regarding occult sphincter rupture.