Objective. To study prevalence and risk factors for anal incontinence (AI) after obstetric anal sphincter rupture. Material and methods. This was a retrospective clinical observational study. Among 14 959 vaginal deliveries, 591 women were diagnosed with obstetric anal sphincter ruptures (3.9%) at one Norwegian University Hospital in 2003–2005. Patients were examined and interviewed approximately 10 months after delivery. Anal continence was classified with St. Mark's incontinence score (0, complete anal continence; ≥3, anal incontinence), and defects in anal sphincter muscles were diagnosed by endoanal ultrasound. Prevalence of anal incontinence was assessed in relation to obstetrical and maternal characteristics as well as the correlation between anal incontinence and ultrasound-detectable defects of sphincter muscle. Results. Anal incontinence with a St. Mark's score of ≥3 was reported by 21% of women with obstetric anal sphincter rupture, with inability to control gas as the most prevalent symptom. Women with AI were more likely to report urinary incontinence compared with women having no AI. In a multiple regression analysis of maternal and obstetrical risk factors, fourth degree sphincter tear was the only significant risk factor for AI. Anal incontinence was more frequent in patients diagnosed with than without ultrasound-identified anal sphincter muscle defects at 10 months postpartum follow-up. Conclusion. Anal as well as urinary incontinence after delivery with obstetric anal sphincter rupture is common, and prenatal obstetric and maternal variables could not predict anal incontinence. Fourth degree perineal tear and a persistent ultrasound-detected defect in the anal sphincter muscles are associated with AI.