Patients presenting diffuse, advanced, established peritonitis due to free perforation of the colon, in whom an adequate abdominal debridement cannot be obtained in one operative session were selected. We report results of the planned relaparotomy approach in 44 patients as compared with an historical series of 9 analogous patients treated by on demand exploratory relaparotomies. Planned relaparotomies were performed every 2 days until the abdominal cavity became macroscopically clean. This approach significantly reduced both the incidence of multiple organ failure and the mortality rate (31%) as compared with the regimen of on demand relaparotomy. The mortality rate in the planned relaparotomy group is related to the age of the patient and to the nature of peritonitis. Faecal peritonitis carries a higher mortality rate than purulent peritonitis. The mortality rates of severe postoperative peritonitis and advanced primary peritonitis were not significantly different. Surgery for severe, diffuse peritonitis has to be prompt, moderately aggressive and repeated if necessary. Therefore, planned relaparotomies have a place in the treatment of selected patients presenting diffuse, advanced, established peritonitis.