Although reports on the positive effects of fitness and exercise predominate in the exercise literature, some researchers describe frequent exercise as compulsive or addictive behavior. This paper addresses these "negative addictions" of exercise. As early as 1970, researchers recognized the addictive qualities of exercise. Short-term studies on exercise found salutary effects on self-esteem and mood, but these studies tended not to continue long enough to detect an addictive process. However, case studies and experiments on the effects of depriving athletes of activity have documented the appearance of withdrawal symptoms. In the last decade, investigations into the psychological and addictive effects of exercise have become more common and numerous attempts to quantify the negative addiction to exercise have been attempted. Case reports can provide illustrative data on both the compulsive nature of addicted exercisers and potential causes. Research shows that the exercise addict continues to exercise despite medical, social, and vocational counterindications. Studies reveal that individuals become depressed when prevented from exercising and some reports suggest that periods of emotional stress may provoke addictions to exercise. Likewise, heightened physical activity is viewed as a common feature of eating disorders, such as anorexia nervosa. Researchers still do not understand the etiological mechanism behind addictive exercise. (RJM)