Colonic perforation is an abdominal emergency with high morbidity and mortality. This retrospective study was performed to evaluate the prognostic relevance of several factors and to characterize patients at high risk. One hundred and twelve patients (61 women, 51 men) were treated for colonic perforation from 1979 to 1992. Diverticulitis [65 patients (58%)] and carcinoma [24 patients (21%)] were the commonest pathology. In 62 cases (55%) perforation was found to be covered; 50 (45%) times it was free. 34 (30%) patients had diffuse peritonitis. Resection with primary anastomosis was performed 43 times (7 times with a protective colostomy). Resection without restoration of the intestinal continuity was carried out 53 times (including 49 Hartmann operations). Suture with drainage was performed 16 times mainly after iatrogenic perforation (8 times with a colostomy). The overall mortality was 19.6% (22 patients). The prognostic importance of various factors was investigated by univariate analysis (Wilcoxon and Chi-square test) and stepwise logistic regression including sex, age, underlying disease, localization and type of perforation, degree of peritonitis, pre- or postoperative organ failure, surgical procedure, reoperation, sepsis and the Mannheimer Peritonitis Index (MPI) score. Age over 65 years (relative risk 4.6, P = 0.0089), organ failure (relative risk 40, P = 0.001) and MPI (relative risk for an increase of 10 points 2.72, P = 0.001) proved to be the only risk factors of significance. The patient's course is determined by the septic state, while the underlying pathology and degree of peritonitis did not significantly influence survival.