The addictive aspect of exercise behavior is well known. The issue is controversial, because exercise, unlike tobacco smoking, drinking alcohol, or gambling, is viewed as a healthy behavior. Therefore, it is not surprising that high levels of commitment to exercise were connotated as “positive addiction.” In fact, exercise addiction is a morbid pattern of uncontrolled exercise behavior resulting in harm to the affected individual. It is driven by strong urges and cravings for the behavior, which are also accompanied by severe withdrawal symptoms. Research into exercise addiction is based on self-reports yielding risk scores rather than diagnosis. The prevalence of exercise addiction is rare, ranging between 0.3% and 0.5% in the general population and 3.0% and 6.0% in the exercising population. There are several models for the morbidity, but many of them are incomplete. A more recent interactional model is presented to emphasize the subjective nature of the morbidity. It is stressed that a better understanding of the behavior may result from the inductive examination of idiographic clinical case studies rather than nomothetic research.