A group of 200 morbidly obese men (average weight, 143.5 kg; age, 23 to 70 years) were admitted to a weight control program between 1960 and 1977 and were followed up for a mean period of 7 1/2 years. There was complete follow-up until the termination of the study or until death for 185 men. Fifteen men were followed up for fractional periods. Fifty of the 200 died during the course of the study. Life-table techniques, comparing the mortality among the obese with that among men in the general population, demonstrated a 12-fold excess mortality in the obese in the age group 25 to 34 years and a sixfold excess in the age group 35 to 44 years. This ratio diminished with advancing age. Cardiovascular disease was reported as the cause of death more frequently and malignancies less frequently than they were for men in the US general population.