Fifty-seven patients who were treated conservatively for colonic diverticulitis between 1977 and 1979 were followed for at least 10 years. Twenty-four patients had two or more episodes of diverticulitis, but only three had surgery on a prophylactic basis because of recurrent attacks. None of the patients had any serious complications during the follow-up. During the same period, eight patients with inflammatory pseudotumour underwent elective sigmoid resection and primary anastomosis without complications. --Between 1977 and 1988, forty-eight patients had emergency surgery for septic complications of diverticulitis. The mortality was 17%. Only two patients had had one episode of diverticulitis before the actual emergency. Recurrent diverticulitis rarely causes complications that may need emergency surgery. On the other hand, serious complications of diverticulitis usually are the first clinical manifestation of the disease. Thus, the chances of preventing complications with active prophylactic surgery seem to be limited.