BackgroundThe advisability of performing ileal pouch–anal anastomosis for patients with indeterminate colitis is debated. Indeterminate colitis is found in up to 15% of inflammatory bowel disease colectomy specimens. We determined long-term outcomes in patients diagnosed with indeterminate colitis undergoing ileal pouch–anal anastomosis. MethodsFifty-six patients were included with a mean follow-up of 14 ± 7 years. Long-term behavior was defined based on surgeon assessment as “Crohn disease–like” in patients who subsequently developed clear signs of Crohn disease and as “non-Crohn disease–like.” Long-term function was assessed using the Cleveland Global Quality of Life and Pouch Functional Score. ResultsThirty-nine percent of patients developed Crohn disease–like behavior, and 61% developed non-Crohn disease–like behavior. Both groups experienced a high rate of pouchitis (57%). Crohn disease–like patients required more anti-inflammatory/immunomodulatory medications (95% vs 18%, P < .001), dilatations for afferent-limb strictures (41% vs 0%, P < .001), and pouch reoperations (32% vs 6%, P = .02). Eight patients required pouch excision or diversion (7 with Crohn disease–like behavior). The Pouch Functional Score was equivalent between groups. ConclusionLong-term function after ileal pouch–anal anastomosis for the majority of indeterminate colitis patients was good. Approximately 40% eventually exhibited Crohn disease–like behavior, but the majority had acceptable function and quality of life. Ileal pouch–anal anastomosis is an appropriate surgical option for indeterminate colitis patients after informed consent.