Sigmoid diverticulitis with perforation and generalized peritonitis is a grave complication of diverticular disease. To compare accurately the results of two operative approaches--proximal colostomy with drainage and proximal colostomy with resection or exteriorization--the authors assessed the clinical and pathologic features of 121 consecutive patients with perforating sigmoid diverticulitis. There were no differences between treatment groups in age, sex, mean duration of symptoms, clinical presentation, number of coexistent diseases, type of peritonitis or chronic corticosteroid use. Overall mortality for emergency operation was 12 percent. Mortality was significantly greater (P less than 0.05) among the 31 patients treated by colostomy and drainage (26 percent) than among the 90 patients treated by colostomy and resection or exteriorization (7 percent). Seven of the nine patients who died from persistent sepsis had undergone colostomy and drainage. Four clinical factors were found to be predictive of mortality (P less than 0.05): persistent postoperative sepsis, fecal peritonitis, preoperative hypotension, and prolonged duration of symptoms. These factors identified a subgroup of patients who, because of an increased risk of death, would be likely to benefit from the more complete eradication of the septic focus that is achieved by colostomy and resection.