The patterns of presentation and associated treatments of 65 patients with acute perforated diverticulitis of the left colon have been reviewed. Four types of operations were identified: primary resection with anastomosis (group I, N = 29), primary resection with anastomosis and protective colostomy (group II, N = 5), primary resection with Hartmann procedure (group III, N = 26), and delayed resection three-staged procedure (group IV, N = 5). The severity of disease was also classified (stages I to IV). Postoperative mortality rates in the first two groups were lower than that of the Hartmann group (3.4 vs. 15.3 percent). The mean length of initial hospitalization was 16 +/- 1.2 days for group I, 18.2 +/- 4.4 days for group II, 19.4 +/- 2 days for group III, 26.4 +/- 4.4 days for group IV (P less than .05, t-test group IV vs. groups I, II, and III). Complications in the Hartmann group were high with a 23 percent wound infection rate and mortality after closure of colostomy and bowel reconstruction was 3.8 percent. These data demonstrate that primary resection with anastomosis is a satisfactory operation for the majority of patients with perforated diverticulitis (stages I to III), and there appears to be no clinical indication to use the three-staged operation.