OBJECTIVE: To estimate whether endoanal ultrasound findings are more prevalent in primiparous women with a history of anal sphincter tear than in women without this history and whether the findings are associated with fecal incontinence symptoms. METHODS: A total of 251 primiparous women at seven clinical sites underwent standardized ultrasound assessment of the internal and external anal sphincter 6-12 months after delivery. Participants were women in the three cohorts of the Childbirth and Pelvic Symptoms Study: 1) women with clinically evident third- or fourth-degree tear at vaginal delivery (n=106); 2) no tear at vaginal delivery (n=106); and 3) cesarean delivery without labor (n=39). Women completed the Fecal Incontinence Severity Index to assess fecal incontinence symptoms. RESULTS: Thirty-five percent of the sphincter tear group exhibited internal sphincter gaps compared with 3% of vaginal controls (odds ratio [OR] 18.4, 95% confidence interval [CI] 5.5-62.1) and 10% of cesarean controls. External sphincter gaps were identified in 51% of the tear group compared with 31% of vaginal controls (OR 2.3, 95% CI 1.3-4.0) and 28% of cesarean controls. In the tear group, fecal incontinence severity was greater in those with internal sphincter gaps compared with those with no internal sphincter gaps (Fecal Incontinence Severity Index score 6.6±8.3 compared with 3.3±6.1, P=.02), as well as in those with external sphincter gaps (6.1±8.4 compared with 2.7±5.0, P=.01), and greatest in those with both internal and external sphincter gaps compared with at least one gap not present (7.2±8.1 compared with 3.4±6.4, P=.003). CONCLUSION: Anal sphincter gaps detected by ultrasonography are prevalent in postpartum primiparous women with a history of sphincter tear and are associated with fecal incontinence severity. © 2006 The American College of Obstetricians and Gynecologists.