This article explores recent research in psychology, physiology, endocrinology, and animal behavior that bears on the relationship between compulsive athleticism and the eating disorders. There are several differences and a number of likenesses between these groups. Both groups are composed of persistent, perfectionistic, high-achieving persons. Compulsive (“addicted”) athletes appear healthier than eating-disordered patients on psychological tests, even though the athletes may do or say things that appear irrational. The relationship between compulsive athleticism and the eating disorders can best be described in terms of a risk-factor model. Perfectionistic persons can be easily caught up in a diet or exercise program and can become even more committed through social reinforcement and the formation of a reciprocal feedback loop. When perfectionistic persons engage in extreme exertion while following a restricted, “healthy” diet, this can increase obsessional behavior by affecting mood and cognition. Eating-disordered patients experience similar changes in personality and behavior secondary to stress and dietary restriction.