Twenty-five obese men admitted to the medical and psychiatric clinics of the Hospital of the University of Pennsylvania were studied by a variety of clinical techniques. Marked variability in the behavior of these men was observed, and no common personality type was found which would distinguish them from non-obese men. However, 2 types of obese men could be distinguished by age of onset of their obesity. Men who became obese before adulthood were heavier, had more unstable weight histories, and had higher intelligence quotients than did men who became obese as adults. Furthermore, the obesity of these "juvenile obese" subjects frequently colored their concepts of themselves and tneir bodies in a most derogatory manner, a finding which was not observed in any of the 14 "adult obese" men. In contrast to the relationship of alcoholic intake to obesity in women, this factor played a greater role and physical inactivity a lesser role among these obese men.