The most frequent causes of postoperative peritonitis are circumscribed abscesses, the postoperative ileus and the anastomotic leakage or breakdown of the digestive suture. 2. The mortality is 33%; procedures in upper abdominal surgery are accompanied by higher mortality than in colorectal surgery in cases of postoperative peritonitis. 3. The most frequent cause of death after reoperation is the generalized sepsis. 4. A mixed flora of spores are found in most cases; obligate anaerobic spores are found mostly after colorectal procedures, while typical "hospitalized spores" were present equally after all surgical treatment in abdomen. 5. Method of treatment is: early surgical reintervention, systemic application of antibiotics, peritoneal lavage in generalized peritonitis, sufficient drainage in local peritonitis and the open-wound-treatment of the abdominal cavage in severe forms.