The accumulation of fat in hepatocytes with a necroinflammatory component-steatohepatitis-that may or may not have associated fibrosis is becoming a frequent lesion. Although steatohepatitis is currently recognized to be a leading cause of cryptogenic cirrhosis, the pathogenesis has not been fully elucidated. Among the various factors implicated, intestinal bacterial overgrowth may play a role. Indeed, various rat models of intestinal bacterial overgrowth have been associated with liver lesions similar to NASH, and bacterial overgrowth has been observed significantly more often in patients with NASH compared with control subjects. The authors discuss the relationship among intestinal bacterial overgrowth, steatohepatitis development, and probiotic treatment.