PURPOSE:Ileal pouch‐anal anastomosis (IPAA) is the surgical treatment of choice for most patients with chronic ulcerative colitis. Crohn's disease is, however, a contraindication. Because distinction between UC and Crohn's disease can be difficult, some patients with Crohn's disease inadvertently undergo IPAA. The aim of this study was to determine the long‐term outcome of patients with Crohn's disease who have undergone IPAA.METHODS:A total of 37 patients (20 men) were studied. Each had undergone mucosectomy with handsewn IPAA (J‐pouch, n=35; S‐pouch, n=1; W‐pouch, n=1). Histologic examination of the resected specimen at time of IPAA showed features of ulcerative colitis (n=22), indeterminate colitis (n=9), or Crohn's disease (n=6). The stoma was closed in all patients.RESULTS:A total of 11 of 37 patients developed complex fistulas (pouch‐cutaneous (n=6), pouch‐vaginal (n=4), or pouch‐vesical (n=1). Crohn's disease has recurred in the pouch (n=20), anal canal (n=4), pouch and anal canal (n=10), and elsewhere (n=3). After ten years (range, 3‐14), the pouch remainsin situin 20 patients in whom frequency of bowel movement is seven times (3‐10)/24 hours,in situbut defunctioned in seven patients, and excised in ten patients (failure rate, 45 percent).CONCLUSIONS:Inadvertent IPAA for Crohn's disease is associated with a high rate of failure (45 percent) but an acceptable long‐term functional result if the pouch can be keptin situ.