In the study 52 patients with decompensated liver cirrhosis and "tense" ascites were included. According to the clinical picture, ascites cultures and the number of polymorphonuclears in cmm of the ascitic fluid, all patients were selected in one of the following groups: 1. group of patients with sterile ascites (28), 2. group of patients with spontaneous peritonitis (16), and 3. group of patients with bacterascites (8). The results have shown that the incidence of spontaneous peritonitis is much higher in the group of "tense" ascites patients than in the group of all patients with ascites, the ratio being 30.7% compared to 6% in all cirrhotic patients with ascites. Spontaneous bacterial peritonitis correlates with increased polymorphonuclears in the ascitic fluid (p less than 0.05), decreased pH values (p less than 0.0), and increased amounts of total proteins in the ascitic fluid (p less than 0.05). The lethality rate in the group of spontaneous peritonitis and sterile ascites was 43.7% and 7.1% respectively. Early diagnosis and, of course, adequate therapy are the main points in spontaneous bacterial peritonitis.