Patients with Crohn's colitis are generally not considered candidates for the ileal pouch-anal anastomosis (IPAA) procedure. We reviewed 362 consecutive patients undergoing IPAA and analyzed the outcome of this procedure on 25 patients with a preoperative diagnosis of mucosal ulcerative colitis who were subsequently proven to have Crohn's disease. The mean follow-up was 38.1 months. Sixteen patients have a functioning pouch, seven have required pouch excision, one is diverted, and one has died. Only one of nine patients in whom there was a preoperative clinical feature suggestive of Crohn's disease has a functioning pouch, with complications uniformly occurring within months of ileostomy closure. In contrast, 15 of 16 patients without preoperative features of Crohn's disease have maintained their pouch, generally with good results. These data suggest that patients in whom there is clinical and pathologic evidence of Crohn's disease do very poorly without meaningful symptom-free intervals. However, patients without any clinical features of Crohn's disease, despite a histopathologic diagnosis of Crohn's colitis, have had a good outcome with IPAA thus far.