Background: Secondary peritonitis is a serious complication of all the inflammatory diseases and injuries of the abdominal organs and requires urgent surgical intervention. The mortality rate of patients with secondary bacterial peritonitis (SBP) reaches ۷۰%. In some patients, despite the treatment, secondary peritonitis turns into tertiary peritonitis (TP), which complicates the healing process and aggravates the prognosis. Inadequate drainage of the abdominal cavity is a possible contributing factor to the formation of TP. Aims: A prospective study of the result of surgical treatment of patients with SBP was carried out to improve the results of treatment. Methods. The study included ۶۰۸ patients with SBP who underwent surgery in a clinical hospital in Russia in ۲۰۱۳-۲۰۱۹. All the patients were divided into groups depending on the method of draining the abdominal cavity and on signs of the purulent process generalization, the marker of which was multiple organ failure. Efficiency of abdominal drainage (by the incidence of TP) and of treatment results (in terms of mortality) were assessed in each group. Results: In patients without signs of the purulent process generalization, drainage of the abdominal cavity with drainage tubes (۲۹۳ observations) is accompanied by the development of TP in ۴.۱% of cases and by mortality in ۲۲.۹%. If the purulent process is of a generalized nature (۳۱۵ observations), the incidence of TP increases ten-fold and is ۴۱.۹%, and the mortality rate increases ۲.۷ times and reaches ۶۲.۸%. With the generalization of the purulent process, the efficiency of drainage of the abdominal cavity has a significant impact on the results of surgical treatment of patients with SBP. If abdominal drainage is carried out with drainage tubes (۱۲۹ observations), the incidence of TP is ۴۱.۹%, and the mortality rate is ۶۲.۸%. Drainage of the abdominal cavity using traditional laparostomy (Bogota bag, ۱۰۴ cases) is accompanied by the development of TP in ۳۶.۵% of cases and mortality in ۴۵.۲%. If the abdomen is drained using active laparostomy (VAC-system, ۸۲ observations), the incidence of TP is reduced to ۱۸.۳% and mortality to ۱۹.۵%. Conclusion. Drainage of the abdominal cavity is the most important stage of surgical intervention in patients with SBP. In cases of the purulent process generalization, drainage of the abdominal cavity in the most effective way– by active laparostomy (VAC-system) will improve the results of treatment of these patients.