Diverticular disease occurs when small pouches, called diverticula, are formed in the colon, which is part of the large intestine. This formation of diverticula (also known as diverticulosis) occurs by increased pressure on weakened spots in the intestinal walls. Diverticulosis is very common and occurs in 10 percent of people over age 40 and in 50 percent of people over age 60. Most people will have no or few symptoms from diverticulosis. If one of the pouches becomes blocked with waste, bacteria can build up and cause infection and inflammation; this inflammation of the diverticulum is called diverticulitis. Symptoms of diverticulitis include alternating diarrhea with constipation, painful cramps or tenderness in the lower abdomen, chills, or fever. Serious complications of diverticulitis include abscesses in the abdominal cavity, blockage of the intestines, or a fistula (abnormal connection between two organs).