SummaryThe pathogenesis of colonic diverticulosis still is not well understood. It is believed that it is a combination of the degenerative process of aging, associated with spasm and increased intraluminal pressure. There is strong evidence to support the view that a muscle abnormality with shortening and hypertrophy precedes diverticulosis. An associated increase in the frequency and magnitude of spontaneous contractions causes an increase in internal pressure on the colon wall. Ultimately, this results in herniation and pouch formation. Once the diverticulum has herniated through the wall permanently, the continued increased pressure forces fecal contents into the pouch. This also causes vascular engorgement, necrosis of the mucosa, and bacterial penetration.The actual inflammation of diverticulitis results from perforation, rather than stagnation of fecal material. The shortening of the bowel, with spasm and thickening of the circular muscle, results in diverticular disease, and the common “spastic colon” may well be a precursor of diverticulosis coli.