Obesity is the single most significant risk factor for the development of nonalcoholic fatty liver disease (NAFLD) in children and adults. NALFD is estimated to occur in 30 to 100% of obese adults, and in approximately 53% of obese children. The majority of obese patients have ultrasonographic evidence of fatty liver; 30% have histologically documented nonalcoholic steatohepatitis (NASH). Up to 25% of patients with NASH may progress to cirrhosis. In the United States, an estimated 65% of adults are overweight and 31% are obese. Between 2001 and 2002, the number of people with severe obesity, who are more than 100 pounds overweight, rose to nearly 11 million. Since 1970, levels of childhood and teen overweight have climbed to approximately 16% in those aged 6 to 19 years. Recent findings indicate that key features of NAFLD and NASH improve or resolve dramatically with weight loss. This article discusses weight loss surgeries and their effects on liver disease.