Obesity increases the risk and severity of liver disease. The most common form of liver disease that occurs in obesity is NAFLD. A better understanding of the basic disease mechanisms and natural histories ofNAFLD is needed to guide management and treatment of obese patients and others with this disorder. Large, prospective, randomized, controlled treatment trials also are needed. Ideally, such studies will focus on well-defined patient subsets and monitor the impact of therapy on clinically relevant endpoints, such as liver-related morbidity and mortality.