Pouchitis is a poorly defined syndrome that is unique to patients with an ileal reservoir. During a prospective follow-up review of 215 patients who underwent ileal pouch-anal anastomosis, pouchitis was diagnosed in 30 patients (14 percent). Based on the clinical course, two distinct patterns of pouchitis were recognized: patients who experienced two or fewer episodes (Group 1-18 patients) and patients who experienced at least three episodes (Group 2-12 patients). Histopathologic review of resected colons revealed a preponderance of indeterminate colitis in patients in Group 2 (58.3 percent) compared with patients in Group 1 (0 percent). In Group 1; 88.9 percent of patients responded to therapy with metronidazole. Only 25 percent of patients in Group 2 responded to metronidazole alone. Most patients in Group 2 required sulfasalazine, topical steroids, or both. Of the 30 patients with pouchitis, four (13.3 percent) had a distinct endoscopic pattern of distal inflammation. This subset of patients with short strip pouchitis was successfully treated with topical steroid preparations. The clinical differences suggest different causes of pouchitis in these two groups.