Nonalcoholic fatty liver disease (NAFLD) is being increasingly recognized as one of the most common chronic liver diseases. The natural history of this liver disease remains unclear due to its indolent nature, the paucity of prospective studies, and the lack of consensus regarding the various forms of this disorder. Based on retrospective studies, it appears that the histologic features of NAFLD may be important determinants of the clinical course of this disease; patients with nonalcoholic steatohepatitis (NASH) appear to have a higher likelihood of progression to cirrhosis. There is an increased risk of hepatocellular carcinoma and end-stage liver disease among patients with NASH-related cirrhosis and those with cryptogenic cirrhosis, which likely represents a late stage of NAFLD. Recurrence of NASH has been described among patients who have undergone liver transplantation for NASH-related end-stage liver disease.