Nonalcoholic fatty liver disease is an increasingly prevalent disorder that spans a range of conditions from hepatic steatosis to cirrhosis. It is commonly associated with obesity and diabetes, two components of the metabolic syndrome. Although hepatic steatosis may be reversible, disease progression appears to be triggered by overproduction of reactive oxygen species and mitochondrial injury in hepatocytes. Evolving treatments are focused on reversing insulin resistance, which underlies many of the metabolic derangements in this disease.