Although excessive physical activity and obsessive compulsiveness are both prevalent in anorexia nervosa (AN), to date, the association between these two factors has not been systematically investigated. The aim of the present study was to investigate the relationship between obsessive compulsiveness and both behavioral and psychological aspects of exercise in women with AN, and to compare them to a nonclinical sample of females classified as either moderate or high-level exercisers. Results indicated that obsessive compulsiveness, weight preoccupation, and pathological aspects of exercise were significantly related to the level of physical activity among the eating disorder patients. For the high-level exercisers, only obsessive compulsiveness was significantly related to the amount of physical activity. The findings are discussed in terms of a model in which physical activity, starvation, and obsessive compulsiveness are reciprocally and dynamically related, with each factor creating a destructive bidirectional loop that is resistant to change and difficult to break. We propose that this self-perpetuating loop may be a significant influence in the development and maintenance of eating disorders in a certain subgroup of women.