Obesity, or the presence of a body mass index exceeding 30 kg/m2, has assumed epidemic proportions in the United States. More than a cosmetic issue, obesity is associated with many comorbidities that contribute to multiple organ dysfunction, illness, and shortened life span. This review covers new and emerging information on the relationship of obesity to common and debilitating hepatic and gastrointestinal disorders, including nonalcoholic steatohepatitis, gastroesophageal reflux, gallstones, and increased risk of colon cancer. Understanding the role of obesity in these disorders should lead to new insights into the pathogenesis of common liver and gastrointestinal diseases and to new treatment strategies for the practicing gastroenterologist.