Planned and "on-demand' reoperations are well-established concepts in the management of severe diffuse peritonitis. Both concepts were applied at our surgical department and reviewed with regard to specific complications and lethality. In the period between 1 January 1989 and 31 May 1994, 62 patients with the diagnosis of diffuse peritonitis underwent operative treatment at our surgical department. The mean age of the 29 female and 33 male patients was 58.2 years (range 17-93 years). The origin of peritonitis was the stomach in 8.1%, duodenum in 16.1%, small intestine in 12.9%, large intestine in 41.9% and the pancreas in 16.1%. Among these 62 patients, 15 were reoperated upon according to plan and 47 were reoperated upon on demand. The intraoperatively gained Mannheim peritonitis index and the Apache II score were similar in both groups. The average number of reoperations was five in the group of planned revisions and three in the group of on-demand revisions. Also lethality was similar in both groups. Regarding lethality, only the age of the patient (P < 0.03) and the preoperative Apache II score (P < 0.01) reached statistical significance. As expected, eradication of the infectious source was the precondition of survival regardless of the type of reoperation. Regarding our results, we conclude that planned or on-demand reoperations lead to similar results in the treatment of diffuse peritonitis. The crucial point for success is that elimination of the infection source take place as soon as possible.