Diverticular disease (diverticulosis) is a condition causing abnormal small pouches, also known as diverticula, to form in the wall of the large intestine. The formation of these pouches are a result of constant pressure to the bowel wall or weakened muscles. Although these pouches can form anywhere in the colon, they are most common in the sigmoid colon. Diverticula are different to polyps and are not cancerous.