Resection is the preferred method of perforated diverticular disease treatment compared to conservative treatment. However, the immediate or deferred timing of bowel continuity restoration for advanced degrees of peritoneal contamination is debatable. This is a retrospective study designed to identify operative mortality predictors and guidelines for safe primary anastomosis. A pathophysiological score (acute physiology and chronic health evaluation, APACHE II) was applied to 135 consecutive patients who had undergone surgery for acute inflammatory complication of diverticular disease. A multivariate analysis was used to identify prognostic factors such as age, chronic diseases, neoplastic cancer, Acute Physiology Score (APS), Hinchey's classification and APACHE II scores. Seventy patients underwent primary resection and anastomosis, 35 underwent Hartmann's procedure and 15 conservative treatment. There was a significant correlation between operative mortality and increasing disease severity based on Hinchey's classification, APS and APACHE II scores. The multivariate analysis proved APACHE II scores to be the only prognostic factor of operative mortality. Both single and multivariate analysis of variance failed to identify a factor significantly associated with surgical and/or medical postoperative complications. APACHE II scores were the best predictor for operative mortality in patients with diverticular disease complications, but none of the classification criteria used was effective in predicting postoperative complication. Patients with phlegmonous sigmoiditis can be safely treated with primary resection and anastomosis. Conservative treatment should not be considered an effective method for diverticular disease. A prospective trial comparing resection with and without colostomy should be done for local and diffuse purulent peritonitis treatment. Hartmann's procedure is seen to be the only indicator for faecal peritonitis.