Of the 107 patients with complicated diverticulitis operated from 1973-1986 47 were females and 60 males. In 14 of the 107 patients a perforated diverticulitis with diffuse purulent/faecal peritonitis was found, a perforated diverticulitis with localized purulent peritonitis/paracolic abscess in 68 patients and an acute phlegmonous diverticulitis without perforation in 25 patients. Additional pathologic findings were internal fistulae (13 patients), necrotizing fasciitis (3 patients), obstruction (3 patients) and synchronous carcinoma (7 patients). The overall mortality of the 107 patients was 9.3% (= 10 patients) and the morbidity of the 97 survivors 34% (= 33 patients). The mortality of the 14 patients with perforated diverticulitis and diffuse purulent peritonitis was 50% of the 68 patients with perforated diverticulitis and localized purulent peritonitis 4.4% and of the 25 patients with acute phlegmonous diverticulitis 0%. Seven of the 10 patients died after operation of the perforated diverticulitis with diffuse purulent peritonitis - 1 (5) after primary resection with primary anastomosis. 3 (5) after Hartmann procedure, 3 (4) after loop colostomy alone. Three patients died after operation of the perforated diverticulitis with localized purulent peritonitis - 2 (6) after Hartmann procedure, 1 (5) after loop colostomy alone. In spite of forcing the primary resection with primary anastomosis in the years from 1980 - 1986 the mortality decreased for these operations from 35.7% in 1973 - 1979 to 0% in 1980 - 1986. The indication of primary resection with primary anastomosis is justified also for perforated diverticulitis with localized and diffuse peritonitis.