The colon is a long tube-like structure approximately 6 feet in length that stores and then eliminates waste material left over after digestion of food in the small intestine takes place. It is thought that pressure within the colon causes bulging pockets of tissue (sacs) that push out from the colonic walls as a person ages. A small bulging sac pushing outward from the colon wall is called a diverticulum. More than one bulging sac is referred to in the plural as diverticula. Diverticula can occur throughout the colon but are most common near the end of the left colon, referred to as the sigmoid colon, in Western countries. In Asia, the diverticula occur mostly on the right side of the colon. The condition of having these diverticula in the colon is called diverticulosis.

Diverticula are common in the Western world but are rare in areas such as Asia and Africa. Diverticula increase with age. They are uncommon before the age of 40, but are seen in more than 74% of people over the age of 80 years in the U.S. A person with diverticulosis usually has few or no symptoms. The most common symptoms associated with diverticulosis are abdominal pain, constipation, and diarrhea. In some of these patients the symptoms may be due to the concomitant presence of irritable bowel syndrome (IBS) or abnormalities in the function of the muscles of the sigmoid colon (in which case it is referred to as diverticular disease); simple diverticula should cause no symptoms. Occasionally, bleeding originates from a diverticulum, and it is referred to as diverticular bleeding.