Background. Spontaneous bacterial peritonitis (SBP) is a life-threatening infection in patients with portal hypertension (PH) and ascites. Its prevention and treatment are vital to improve the prognosis in decompensated PH. Alterations in gut microbiota, gut permeability, and systemic immune dysfunction are cornerstones in the development of SBP in patients with PH. This contributes to the translocation of bacteria from the intestinal lumen to the mesenteric lymph nodes, and then to the portal and systemic circulation from where the ascitic fluid can be colonized with the subsequent development of peritonitis. The purpose was to monitor the course of the disease and determine the possibility of correcting pathological factors of SBP such as bacterial contamination and volume of ascitic fluid, nature of bacterial contamination, increased intra-abdominal pressure, hypoalbuminemia, and to evaluate the role of antibacterial therapy, paracentesis in the treatment of patients with SBP in decompensated PG. Materials and methods. Examination and treatment of 242 patients with ascites who were admitted for emergency medical care were carried out. Diagnostic paracentesis was performed to examine ascitic fluid, which allowed to detect neutrophilia > 250 cells in 1 mm3 in 194 (80.2 %) patients and indicated the presence of SBP. These patients made up the first group of observation. In the second group, there were 48 (19.8 %) patients with no clinical and laboratory signs of SBP at the time of hospitalization. Methodology of analysis of actual research material: to find a statistical difference between the distribution of nominal data of patients in this study, we used Pearson’s χ2 test. To establish the strength of the relationship between variables, we determined the polychoric correlation coefficient. When a statistically significant difference was detec-ted, a stratification analysis was performed with determination of the 95% confidence interval of the odds ratio (Clopper-Pearson method) and the risk ratio for the development of complications in PH. Results. Empiric antibacterial therapy, which was carried out from the moment of receiving information about SBP and began with the use of broad-spectrum antibiotics, was successful in 41 % of cases that was confirmed by repeated examination of ascitic fluid. In antibiotic resistance, determining the sensitivity of ascitic microflora led to a delay in an effective anti-inflammatory treatment and affected the results. In the first group, 39 (20.1 %) patients died, in the second group, 22 (50 %), total mortality was 25.2 %. Conclusions. Diagnostic paracentesis combined with the assessment of bacterial contamination of ascitic fluid, evaluation of intra-abdominal pressure, state of osmoregulation based on albumin concentration is a safe and informative method of diagnosing the severity of pathological process in patients with complicated PH. Treatment of SBP requires urgent care, both in terms of elimination of the infectious factor, and normalization of the disturbed mechanisms of reabsorption regulation by peritoneal and hepatorenal processes. High mortality in patients with SBP is due to the development of inflammation in the abdominal cavity against the background of progressive hepatorenal insufficiency and the inability to correct decompensated PH.