Biofeedback therapy improves symptoms in patients with constipation and obstructive defecation. Whether it also improves anorectal function is unclear. Our purpose was to investigate prospectively the effects of biofeedback therapy on subjective and objective parameters of anorectal function in 25 consecutive patients with obstructive defecation. Biofeedback therapy consisted of pelvic floor relaxation exercises (phase I) and neuromuscular conditioning of rectal sensation and rectoanal coordination, with a solid state manometry system and simulated defecation maneuvers (phase II). The number of sessions was customized for each patient. Clinical improvement was assessed from the changes in anorectal manometry, balloon (50 cc) expulsion test, and the symptom and stool diaries. The number of therapy sessions varied [mean (range) = 6 (2-10)]. After therapy, when straining as if to defecate, the percentage anal relaxation, intrarectal pressure, and defecation index increased (P < 0.001). The balloon expulsion time, laxative consumption, and straining effort decreased (P < 0.001). Before therapy, 16/25 (64%) patients had impaired rectal sensation, and after therapy this improved (P < 0.001). After therapy, 15/25 (60%) patients reported > or = 75% satisfaction with bowel habit and 8/25 (32%) reported > or = 50% satisfaction (P < 0.001); 15/16 (94%) patients discontinued digital disimpaction. Biofeedback therapy not only improves subjective but also objective parameters of anorectal function in at least 76% of patients by rectifying the underlying pathophysiologic disturbance(s). Sensory conditioning and customizing the number of sessions may offer additional benefits.