Hepatic encephalopathy, bacterial infections and endotoxemia in cirrhotic patients have been related to colonic flora. However, an abnormal small bowel bacterial content could also be implied. We investigated small bowel bacterial overgrowth (SIBO) by jejunal cultures in 14 cirrhotic patients and 5 control subjects, and indirectly by the lactulose H2 breath test in 22 patients with cirrhosis and 12 controls. SIBO was demonstrated by cultures in 64% of cirrhotic patients and 1 of 5 controls. The breath test was positive for SIBO in 45% of patients with cirrhosis and 8% of controls. No differences were noted between patients with alcoholic and non-alcoholic liver disease. According to fasting H2 breath levels, SIBO was significantly correlated with the Child-Pugh score for hepatic function (r = 0.45; p < 0.05). Also, patients with positive criteria for SIBO in jejunal cultures had worse hepatic function in comparison to cirrhotics with normal jejunal bacterial counts (p < 0.05). Thus SIBO is frequent in patients with hepatic cirrhosis and is associated with impairment in hepatic function.