Diverticulosis of the colon and its clinical sequelae--diverticulitis, peridiverticulitis, and pericolitis--are typical diseases of elderly people. The main causes are weakness of the connective tissue in the colonic wall increasing with age and pathologic motility pattern of the colon due to low dietary fibre consumption. In about 20% of all people with diverticula, acute or chronic-recurrent diverticulitis develops, often with serious complications as perforation, abscess or fistula formation, obstruction, inflammatory pseudotumor and intestinal bleeding. Diagnosis is mainly based on clinical examination and barium enema (double contrast, maximal spasmolysis). Colonoscopy may be helpful in excluding carcinoma of the large bowel. Patients with diverticulosis and uncomplicated diverticulitis should be managed conservatively by medical treatment. The following measures proved to be successful: high-fibre diet, unprocessed wheat bran, and hydrophilic plant colloids to regulate the bowel movements, systemic or local antibiotics if signs of inflammation are present, and antispasmodics or analgesics against abdominal pain. Prognosis depends mainly on the duration of the disease, sufficient dietary-fibre intake, and elective or semi-elective surgical intervention before the development of life-threatening complications. The question as to whether diverticula or relapsing attacks of diverticulitis can be prevented with added dietary-fibre remains open for the time being.