Anal manometry before and after surgical repair on a homogeneous group of patients with anterior sphincter defect caused by obstetric injury defined the parameters affected by the repair to achieve anal continence. Between November 1985 and April 1989, 28 patients who underwent anterior anal sphincter reconstruction were studied using anal manometry and were graded for continence. Anal function was improved for 27 of 28 patients (96 percent) relative to their preoperative symptoms, and total control of solid and liquid stools was restored in 21 patients (75 percent). Anal manometry demonstrated that complete control of continence could be achieved if anal sphincter length, resting pressure, and squeeze pressure were restored to normal. Our results showed that sphincter length was improved in 20 patients (71 percent), resting pressure in 16 patients (57 percent), and squeeze pressure in 22 patients (79 percent). The most important factor in achieving normal function of the anal sphincter is restoration of a normal squeeze pressure.