A prospective randomized trial was performed to compare complications and function after hand sewn ileoanal anastomosis with mucosectomy (group A) with stapled ileoanal anastomosis without mucosectomy (group B) during restorative proctocolectomy. Thirty-two age- and sex-matched consecutive patients under the care of one surgeon were randomized. The median duration of anal dilatation while making the anastomosis was 19 min (range 14-33 min) and 1 min (range 0-39 min) in groups A and B respectively (P less than 0.005). The median level of the anastomosis was at the dentate line (range 0-0.5 cm) in group A and 2 cm above the dentate line (range 0.2-4.0 cm) in group B (P less than 0.005). Seven patients in group A and 11 in group B had at least one postoperative complication (n.s.). One patient in group A and four in group B developed an anastomotic stricture requiring dilatation (n.s.). One patient in group B had the reservoir removed. Function was assessed at a median of 11 months (range 7-15 months) after ileostomy closure in 14 patients in group A, and at a median of 12 months (range 5-17 months) in 14 patients in group B. Median frequency of defaecation per 24 h was 4 in both groups (group A, range 2-7; group B, range 2-10). Night evacuation (greater than once per week) occurred in seven patients in each group. All patients in both groups could delay the desire to defaecate by more than 30 min. Eleven patients in group A and 12 in group B had normal continence. Evidence to date favours a full mucosectomy. Function is not vitiated by this technique and surgical removal of the disease is more complete.