Whereas most individuals with nonalcoholic fatty liver disease (NAFLD) will have steatosis, only a minority will ever develop progressive disease. Family studies and interethnic variations in susceptibility suggest that genetic factors may be important in determining disease risk. Although no genetic associations with advanced NAFLD have been replicated in large studies, preliminary data suggest that polymorphisms in the genes encoding microsomal triglyceride transfer protein, superoxide dismutase 2, the CD14 endotoxin receptor, tumor necrosis factor-α, transforming growth factor-β, and angiotensinogen may be associated with steatohepatitis and/or fibrosis. With the advent of high-throughput gene analyses and the reduced cost of whole genomewide scans, it seems likely that genes contributing to inherited susceptibility to this common disease will be identified in the near future.