The risk of de novo Crohn's disease (CD) after ileal pouch-anal anastomosis (IPAA) for ulcerative colitis (UC) versus inflammatory bowel disease unclassified (IBDU) or indeterminate colitis (IC) remains debatable. Here, we present updated results after long-term follow-up of a previously studied cohort of 334 patients with UC, IBDU, or IC who underwent IPAA during a 10-year period ending 2007. Of 334 study patients, 56 per cent were male and median age was 38 years (range: 8-81). Patients were classified as UC (n = 237) or IBDU (n = 97) preoperatively and UC (n = 236) or IC (n = 98) postoperatively. After a median follow-up of 76 months (range: 3-236), 63 patients (19%) developed CD within a median of 22 months (range: 1-213) from ileostomy closure compared with the previously published 40 patients (12%) with 26-month follow-up (P = 0.01). The development of de novo CD was similar for patients undergoing IPAA for UC (n = 40; 17%), IBDU (n = 21; 22%) or those classified as having UC (n = 42; 18%) or IC (n = 19; 19%) postoperatively; P > 0.05. Thus, patients with IBDU and IC can expect equivalent long-term outcome to patients with UC after IPAA. Pouch failure occurred in 13 (4%) study patients and was equal among all four groups.