Objective: To gather, synthesize, and present useful scientific information concerning the anal continence mechanism that will aid obstetrician-gynecologists in managing vaginal birth and evaluating women with anal incontinence not caused by disruption of the external anal sphincter.Data sources: Sources included a Medline search and reference lists of relevant research articles and standard textbooks.Methods of study selection: Articles were identified that contained scientific data on the pathophysiology of anal incontinence, the influence of vaginal delivery on the continence mechanism, and therapeutic measures. Only those presenting original research results were included. Studies concerned exclusively with surgical management of the ruptured perineum were excluded.Data extraction and synthesis: All articles were reviewed and the physiologic data summarized. These findings were grouped by their relevance to each anatomical or physiologic issue involving anal incontinence and by whether they considered the issue of injury at the time of vaginal delivery. The data were then assembled into a functionally oriented overview of the continence mechanism. The subject of injury at the time of vaginal delivery was considered separately against a background of continence pathophysiology. Conclusion: Vaginal delivery may initiate damage to the continence mechanism by direct injury to the pelvic floor muscles, damage to their motor innervation, or both. Additional denervation may occur with aging, resulting in a functional disability many years after the initial trauma. These factors should be kept in mind when conducting vaginal birth and planning therapy for anal incontinence.