Ileal pouch-anal anastomosis (IPAA) is currently an alternative to proctocolectomy and ileostomy for patients with ulcerative colitis or familial polyposis. Some studies have suggested significant anal sphincter damage after mucosal proctectomy. Our aim was to assess prospectively late sphincter function after IPAA. In 250 patients, anorectal pressures were assessed with a pneumohydraulic perfused catheter manometry system. Each patient underwent colectomy, mucosal proctectomy, ileoanal anastomosis of a 15 cm ileal J-pouch, and loop ileostomy. Eight weeks after IPAA, anal manometry was repeated, and the ileostomy was closed. Manometry was repeated at yearly intervals. A decline in resting tone of the anal sphincter occurred early after IPAA with a gradual recovery toward control. External sphincter squeeze after pressures were not affected by IPAA and steadily increased to 8 years after operation. During this time, a progressive increase in J-pouch capacity was noted, and 24-hour stool frequency declined from 7.9 +/- 0.3 stools to 6.5 +/- 0.3 stools (p less than 0.05). We conclude that mucosal proctectomy results in internal anal sphincter trauma but is associated with long-term sphincter recovery, coupled with a significant improvement in external sphincter capacity, ileal pouch volume, and stool frequency.