Spontaneous bacterial peritonitis is a hematogenic infection of ascitic fluid occurring in immunodeficient patients with decompensated liver cirrhosis. The most common causative organisms of this monobacterial infection include enterobacteria and Gram-positive cocci. Clinical features are varied and typical signs of infection may be absent. The diagnosis is supported by a significant increase of white blood cells count in ascitic fluid. The therapy of choice is cefotaxime 2 g/8 h. The recurrence rate of spontaneous bacterial peritonitis in the first year is 70%. Recurrence is preventable by intestinal decontamination with norfloxacin.