Typically, patients with spontaneous bacterial peritonitis (SBP) have a single infecting organism of gut origin in the fluid. This pattern is in marked distinction to patients with secondary infection of the ascites, as may occur after traumatic gut perforation, for instance, in which a polymicrobial infection is typical. The onset of spontaneous bacterial peritonitis may be subtle, with only mild abdominal discomfort or general clinical deterioration, including worsening hepatic encephalopathy, renal failure, or a nonspecific “septic” picture. Significant fever may be lacking. The most important diagnostic study is abdominal paracentesis. An ascitic polymorphonuclear leukocyte count greater than 250/cm3 suggests the diagnosis, although it should be noted that a low count does not rule out the diagnosis, and bacterial culture remains the gold standard.