Obesity is the most prevalent and serious nutritional disease among western countries and is rapidly replacing undernutrition as the most common form of malnutrition in the world. Approximately 300,000 deaths a year are currently associated with overweight and obesity, second only to cigarette smoking as a leading cause of preventable death in the United States. Obesity effects 9 organ systems and is a risk factor for gastroesophageal reflux disease, nonalcoholic fatty liver disease, cholelithiasis, and colon cancer. Evidence-based guidelines on the identification, evaluation, and treatment of overweight and obesity have recently been developed by the National Institutes of Health to help practitioners effectively manage their patients. The body mass index is used to classify weight status and risk of disease. Treatment for obesity includes lifestyle management, consisting of diet therapy, physical activity, and behavioral modification, and may include pharmacotherapy or surgery based on level of risk. Currently only 2 medications, sibutramine and orlistat, are approved for long-term use. An initial weight loss of 10% of body weight achieved over 6 months is a recommended target. This article reviews the evaluation and management of the adult obese patient.