In spite of the availability of new powerful antibiotics, intraabdominal sepsis still has a high mortality rate (20-50%). With regards to postoperative peritonitis, the referred high mortality rate is due to a late recognition and a consequently late treatment. The causes for late diagnosis are: uncertain clinical picture; misuse of analgesic drugs; reluctance of the surgeon to accept a failure. Moreover, many operated patients are under treatment with antibiotics: their misuse, particularly broad spectrum ones, is responsible for the selection of resistant bacteria. Age is another very significant prognostic factor: mortality rate is constantly higher in elderly subjects than in younger ones. Malnutrition, immunodepression, origin and location of sepsis, concomitant diseases, immunosuppressive treatments, delayed diagnosis, all can significantly affect clinical outcome. Probably the most important and less assessable factor is represented by the surgeon himself with his experience and technical accuracy: any mistake may worse patient's prognosis. Recently, many Authors have stressed the pathogenic relevance of the intestinal mucosa as a barrier, which may influence the clinical course.