Aim: to investigate the effect of determining the degree of intoxication in peritonitis on the results of treatment of patients. Matherials and methods. The study included 265 patients with peritonitis who were treated in the surgical department of Brovary Multidisciplinary Clinical Hospital during 2020: 141 (53.2%) men and 124 (46.8%) women. Results. In 194 (73,2%) patients, the Mannheim peritoneal index was grade I, among them there were no fatalities, in 63 (23.8%) patients the II (mortality was 1.6%) and in 8 (3.0%) patients — the III degree was determined (mortality was 50.0%). Execution of programmed remediation of the abdominal cavity in patients with stage III Mannheim peritoneal index reduced the mortality by 2 times compared with the prognostic. Conclusions. Of great importance for the course of peritonitis is the syndrome of endogenous intoxication, the progression of which occurs multiorgan failure. Therefore, it is very important to predict the course of peritonitis using a variety of scales, especially APACHE II and the Mannheim peritoneal index, which allow to choose the right treatment tactics.