Over a 6 year period, between January 1992 and December 1997, 30 patients with nontraumatic colorectal perforations undergoing laparotomy were reviewed. The aim of this study was to evaluate predictions on the prognosis using the Mannheim Peritonitis Index (MPI) and to evaluate the risk of this complication. The mean age of the patients was 56.4 years (range 16-88 years). The male:female ratio was 19:11. All patients showed signs of peritonitis and underwent emergency operations. In 50% (15) of the patients, tumor was the cause. According to the MPI scoring, there were 18 patients with an MPI score of 26 or less and 12 patients with an MPI score of 27 or more. For patients with a score less than 27 the mortality rate was zero (0/18) and for score greater than 26, 66.6% (8/12). Overall mortality was 26.6% (8/30). Of 15 patients with perforated colorectal cancers, four patients died (26.6%). The mortality rate for benign perforations was 26.6% (4/15) also. In conclusion, colorectal cancers are the most common cause of the non-traumatic colorectal perforations. Patients with an MPI score greater than 26 represent the highest risk group.