Peritonitis is a severe illness with a high mortality rate and different treatment modalities. Over a time period of 12 years 510 patients with peritonitis treated with continuous peritoneal lavage (CPL) were retrospectively analyzed. 315 of 510 patients with a mean age of 57.4 and a mean APACHE-II-Score of 10.2 on admission had a diffuse four quadrant peritonitis. 195 had a local and diffuse peritonitis due to perforation of the appendix. 232 of 315 patients with diffuse peritonitis (73.7%) had a secondary peritonitis, mostly due to organ perforation. The most frequent comorbidities were congestive heart failure (36.8%), pulmonary diseases (26%), diabetes mellitus (18.7%), chronic renal failure (16.8%), chronic liver diseases (9.5%) and a history of alcohol abuse (12.4%). On admission 18.7% had pulmonary insufficiency, 18.4% renal failure, 14.3% congestive heart failure and 13.3% hepatic insufficiency. 14% had one organ-, 6.7% two organ-, 2.5% three organ- and 5% four organ failure. The mean duration of lavage was 5.1 days with a fluid amount of 8-24 l/day. 81.3% of all patients could be treated successfully. 46 patients were reoperated due to persistent peritonitis. The mortality rate of the primarily treated patients was 15.6% compared to 37.0% of patients who had to be reoperated. The mortality rate of all patients was 18.7%. The prognosis of the clinical outcome was significantly influenced by preexisting organ failure and by the duration of the peritonitis on admission. Our results on CPL for diffuse peritonitis are in accordance with results from other treatment modalities; a direct comparison was not possible due to the different patient groups.