Background: Anal incontinence leads to impairment of the quality of life and lower self-esteem with implications for social, physical, and sexual health; anal incontinence after vaginal delivery is a major concern for many women. Only about half of the cases of postpartum anal incontinence can be related to anal sphincter injuries, and the remaining cases must thus be related to other factors. Objective: The aim of this study was to examine the association between maternal and obstetric characteristics, including the degree of perineal rupture and anal incontinence 12 months postpartum. Furthermore, the aim was to investigate the association between anal sphincter muscle defects, perineal length, and perineal strength and the risk of anal incontinence. Materials and Methods: We conducted a prospective cohort study at 4 Danish hospitals: Odense University Hospital, Aarhus University Hospital, Esbjerg Hospital, and Kolding Hospital. Baseline data were obtained 2 weeks postpartum in relation to an evaluation of perineal wound healing. Symptoms of anal incontinence were evaluated 12 months postpartum by a Web-based questionnaire (St. Mark's incontinence score questionnaire). In addition, defects in the anal sphincter muscles were examined using endoanal ultrasound, perineal length was measured, and perineal strength was examined using anal manometry. The main outcome measurement was anal incontinence defined as a St. Mark's score of >4. We performed multivariate analyses to investigate the risk factors for anal incontinence and to investigate the risk of anal incontinence according to endoanal ultrasound scanning and anal manometry findings. Results: A total of 603 primiparous women (203 with no/labia/first-degree ruptures, 200 with second-degree ruptures, and 200 with third-/fourth-degree ruptures) were included between July 2015 and January 2018. At 12 months postpartum, 575 women (95%) answered the questionnaire; 193 with no/labia/first-degree ruptures, 193 with second-degree ruptures, and 189 with third-/fourth-degree ruptures. A total of 499 women underwent an endoanal ultrasound scanning and 482 women underwent anal manometry. Anal incontinence with a St. Mark's score of >4 was reported by 7% and 9% of women with no/labia/first-degree ruptures or second-degree ruptures, respectively, and by 14%, 15%, 35%, and 33% of women with ruptures of degree 3a, 3b, 3c, and 4, respectively. Compared to women with no or minor tears, women with anal sphincter ruptures had a higher risk of anal incontinence (adjusted relative risk, 2.46; 95% confidence interval, 1.28–4.71). Ruptures of degree 3c and 4 were associated with a substantial increase in risk of anal incontinence (adjusted relative risk, 4.74; 95% confidence interval, 1.98–11.3; and adjusted relative risk, 2.23; 95% confidence interval, 1.59–11.3, respectively), especially if a defect in the external or internal anal sphincter muscle was present (adjusted relative risk, 4.74; 95% confidence interval, 1.54–14.5; and adjusted relative risk, 6.58; 95% confidence interval, 3.35–12.9, respectively). The risk of anal incontinence increased by 8% per 1-unit increase in body mass index (adjusted relative risk, 1.08; 95% confidence interval, 1.03–1.14). Conclusion: Obesity with body mass index of >29.9 and a high-degree rupture (3c or 4), especially with a persistent defect in the internal or external anal sphincter muscle, increased the risk of anal incontinence.