OBJECTIVE The clinical usefulness of assessing anorectal physiology has not been systematically examined. Our aims were to evaluate whether manometric tests of anorectal function influence the management and outcome of patients with defecation disorders, and to identify the patients who may most benefit from this assessment. METHODS Using a standard protocol of anorectal manometry rectal sensation, saline continence, simulated defecation, and pudendal nerve terminal latency tests, we studied 143 consecutive patients (m/f = 27/116) and followed their progress over 18 months. RESULTS Tests of anorectal function in 126 (88%) patients revealed new information that led to a change in the management of 108 (76%) patients. Among 69 patients referred with constipation, 33 (48%) had obstructive defecation, and 40 (58%) had impaired rectal sensation; 30 (43%) improved after biofeedback therapy. Among 56 patients referred with fecal incontinence, 55 (98%) had manometric abnormalities: 30 (53%) had a low squeeze sphincter pressure, 20 (36%) had impaired rectal sensation, and 28 (50%) had pudendal neuropathy. Thiry-four (60%) patients were referred for biofeedback therapy and 11 (20%) for surgery. Of these 15 completed biofeedback therapy with improvement, and six had successful surgery. Seven of 10 (70%) patients referred for preoperative evaluation had abnormalities that contraindicated surgery. CONCLUSIONS Manometric tests of anorectal function provide not only an objective diagnosis but, also, a better understanding of the underlying pathophysiology. In addition, it provides new information that could influence the management and outcome of patients with disorders of defecation.