Diverticulitis is inflammation of an abnormal pouch (diverticulum) in the intestinal wall, usually found in the large intestine (colon). The presence of the pouches themselves is called diverticulosis.

Small protruding sacs of the inner lining of the intestine (diverticulosis) can develop in any part of the intestine. They are most common in the colon. These sacs, called diverticula, occur with increasing frequency after the age of 40. When they become inflamed, the condition is known as diverticulitis.

Diverticulitis is an inflammatory condition where the area around the diverticula becomes irritated and attracts immune cells. It affects 10% to 20% of those with diverticula at some time. These areas can become infected. Risk factors are older age and history of diverticula or prior episodes of diverticulitis. Eating a high-fiber diet and avoiding seeds and nuts may prevent episodes.