Obesity is epidemic in America. About 80 million Americans are obese, 33.4% of adults and about 20% to 25% of children. Obesity produces morbidity and mortality: there are 300,000 obesity-related deaths annually in America. The definition of obesity has not been standard. Recently, the World Health Organization defined overweight as a body mass index (BMI = kg/m(2)) of 25 and obesity as a BMI of greater than or equal to 30. A BMI of greater than or equal to 35 produces a high risk from obesity and of greater than or equal to 40 produces a severe risk. the presence of complications of obesity (hypertension, diabetes, dyslipidemia, sleep apnea, etc.) increases the risk. Treatments of obesity depend on the severity of obesity, the presence of complications, and the absence of exclusions. Exclusions from obesity treatment include pregnancy, lactation, terminal illness, major mental illness, anorexia nervosa. Eating disorders and major medical disorders are strong cautions for obesity treatment. Obesity with a low or modest health risk (BMI: 25-30) is best treated with a diet lower in calories and fat than the current diet, exercise, and lifestyle modification. With obesity that produces a moderate to high health risk (BMI: 30-35), the above treatments plus a very low calorie diet or obesity drugs may be indicated. High and very high health risk due to obesity may be treated with the above regimen plus obesity surgery. In every category of obesity, the presence of complications of obesity increases the risk and justifies more aggressive forms of treatment. Treatment of obesity with drugs has gained acceptance in recent years. There are no absolute indications for drug treatment. Contraindications include pregnancy and lactation, unstable cardiac disease, uncontrolled hypertension, severe psychiatric disorder or anorexia, and other drug therapy, if incompatible. Cautions include the presence of any severe systemic illness and certain other problems such as closed angle glaucoma. Obesity surgery is reserved as a last resort. Contraindications to surgery and significant mental or physical diseases preclude obesity surgery. Whatever the form of treatment, individualized attention with careful follow-up is mandatory. Obesity is similar to other chronic diseases; if the treatment stops, the disease comes back. (C) Elsevier Science Inc. 1998.