This refers to the clinical entity characterised by the presence of sac-like outpocketings of the colonic mucosa and submucosa through weak points of the muscle layer of the large intestine. This contains both diverticulitis and diverticulosis. Diverticular disease is used to describe a specific clinical disorder with defined radiological and pathological appearance, in which there is a characteristic muscle abnormality, usually, but not invariably accompanied by the presence of diverticula which may or may not be inflamed.