To assess whether the presence of backwash ileitis predisposed to the subsequent development of ileal pouchitis after ileal pouch-anal anastomosis, 131 patients who had the operation were studied. Fifteen patients had nonspecific inflammation in the terminal ileum noted at the time of the operation, while 20 patients subsequently developed pouchitis. No correlation between the two conditions was found. Pouchitis developed in two of 15 patients (13 percent) with backwash ileitis and in 18 of 116 patients (16 percent) without the ileitis (P greater than 0.05). Among the 20 patients with pouchitis only two (10 percent) had had previous backwash ileitis. It is concluded that the presence of backwash ileitis does not predispose to later development of pouchitis, and so does not contraindicate use of the inflamed terminal ileum for construction of the ileal pouch and anastomosis.