BACKGROUND: Overweight and obesity rates continue to increase nationally, generating significant interest in weight-loss therapies to address both the burden of obesity-associated chronic disease and individual concerns about appearance. Effective obesity therapies also have the potential for off-label use and unintended consequences. METHODS: The behavioral, pharmacologic, and surgical therapies for obesity are reviewed. Clinical trial issues common to chronic disease states and issues specific to obesity trials are examined. Finally, study designs for obesity therapy, including populations, control arms, sample size, and duration of therapy, are discussed.