Restorative proctocolectomy with ileal pouch-anal anastomosis has become the surgical treatment of choice for most patients with ulcerative colitis who require surgery. Although the surgical procedure offers a cure in some patients, postoperative inflammatory and noninflammatory complications are common. Pouchitis is the most common long-term complication of the procedure. Pouchitis represents a spectrum of disease processes with heterogeneous risk factors, clinical phenotypes, natural history, and prognosis. Accurate diagnosis and classification are important for proper treatment and prognosis.