A prospective study was undertaken in 17 patients undergoing restorative proctocolectomy for ulcerative colitis (13 patients) or familial adenomatous polyposis (4 patients) to determine relationship between pre- and postoperative anal sphincter function, pouch characteristics and functional results. Postoperatively all manometric parameters were significantly reduced and remained so permanently. Only squeeze pressure rose to normal values again. The most important factor for a favourable functional outcome was pouch volume. A capacious reservoir was associated with a low stool frequency, low risk of incontinence and general success of the operation, as assessed subjectively. Perianal soreness with considerable skin problems occurred frequently when resting and squeeze pressures were markedly reduced postoperatively.