inflammation of the peritoneum, the membrane that lines the abdominal wall and then folds in to enclose the abdominal organs. The condition is marked by an accumulation of cells, pus, and other bodily fluids, such as serum and fibrin, in the peritoneal cavity (between the two folds of the peritoneal membrane) and by abdominal pain and distension, vomiting, and fever.

Peritonitis may be acute or chronic, generalized or localized. Acute peritonitis is usually caused by inflammation elsewhere in the body and may be due to a number of causes, such as bacterial invasion from an infected structure, blood or other fluids from a ruptured organ. A perforated gastrointestinal tract, notably a ruptured appendix, is a common cause of peritonitis.

Treatment of peritonitis is directed toward control of the source of inflammation. Surgery is often necessary to remove the source of infection, such as the appendix, or to repair a perforation. If localized abscesses have developed in the peritoneal cavity, antibiotic therapy and drainage are necessary.