Millions of individuals in the United States and around the world are overweight or obese (severely overweight). When weight increases to an extreme level, it is called morbid obesity. Obesity is associated with diabetes, heart disease, high blood pressure, some types of cancer, and other medical problems. Bariatrics is the field of medicine that specializes in treating obesity. Bariatric surgery is the term for operations to help promote weight loss. Bariatric surgical procedures are considered only for people with severe obesity (having a body mass index greater than 40 [about 100 pounds overweight], or having a body mass index greater than 35 [about 50 pounds overweight] with established complications of obesity) and not for individuals with a mild weight problem. This Patient Page is based on one previously published in the February 10, 2010, issue of JAMA.