The increasing prevalence and far-reaching medical, social, and economical implications of obesity have made it a national health-care crisis in the United States. About one in every three persons is at least 20% above ''ideal'' body weight, and approximately 5% have direct weight-related serious health problems (morbid obesity), including hypertension, hyperlipidemia, coronary artery disease, adult-onset diabetes mellitus, degenerative osteoarthropathy, and obstructive sleep apnea. Morbidly obese patients have an estimated 6- to 12-fold increase in mortality. In addition, they have a substantially diminished quality of life, not only physically but also psychosocially due to overt and occult prejudice. Weight reduction must be aggressively pursued in these patients. Medically supervised weight-control programs have been ineffective because patients cannot maintain pronounced long-term weight loss. In contrast, current operative methods have been proved to be effective in helping patients achieve and maintain permanent weight reduction. Several operations have been designed and assessed; with these procedures, weight loss is achieved by inducing malabsorption, maldigestion, early satiety, or a combination of these outcomes. Although these operations have associated side effects and limitations, the expected benefits outweigh the risks. For optimal results, patients must be carefully selected and treated by a multidisciplinary group.