To establish whether patients with indeterminant colitis (patients with ulcerative colitis whose surgical specimens also show features of Crohn's colitis) have an adverse outcome after ileal pouch-anal anastomosis (IPAA), the authors reviewed the pathologic reports and postoperative status of 514 consecutive patients who underwent IPAA for chronic ulcerative colitis (CUC). Twenty-five patients (5 percent) had features of indeterminant colitis (IC), including unusual distribution of inflammation, deep linear ulcers, neural proliferation, transmural inflammation, fissures, creeping fat, and retention of goblet-cell population. The clinical and functional outcome of these 25 IC patients was compared with that of the remaining 489 CUC patients. The mean follow-up was 38 +/- 18 months. No significant differences in complication rates, pouch function, incidence of "pouchitis," or requirement for pouch excision were detected in the two groups at follow-up. Although the authors are continuing to perform IPAA on patients with IC, a better definition of the IC patient and a more objective, prospective analysis of outcome of IC following IPAA is required before confident and specific treatment policies can be recommended.