Persons 45.4 kg (100 lb) or more above desirable weight have exponential increases in mortality and serious morbidity compared with normal persons. The presence of a complication or an independent coronary risk factor along with obesity increases the mortality further. Among the "threshold conditions" that appear at a critical level of body weight (60% or more above desirable weight), the most important are sudden unexplained death, ventilatory disorders, circulatory congestion, and functional limitations in activities of daily living. Recent epidemiologic data on extreme obesity and data on cardiac dysfunction show impaired quality of life in young, morbidly obese patients. Because of the malignant nature of morbid obesity and the inability to achieve and maintain sufficient weight reduction by non-surgical means, surgery is justified in this population.