The treatment of severe diffuse peritonitis is still associated with a mortality of up to 50 %. Particularly the postoperative peritonitis shows high mortality rates due to septic organ failures. The aim of surgical treatment is the definitive source control followed by removal of fibrin and abdominal lavage of contaminants and infectious fluids. Dependent on the severity of the peritoneal reaction, further treatment consists of primary abdominal closure and relaparotomy on demand, programmed lavage or laparostomy respectively. Septic complications have to be treated by intensive care medicine.