Many patients with anorexia or bulimia nervosa use physical activity as a method to influence weight and shape and/or exercise in a compulsive manner. This form of exercising is associated with a more severe illness and higher relapse rates. In a proof-of-concept study, effects of a newly developed sport therapy program aiming to reduce unhealthy exercising were assessed. Thirty-six patients with eating disorders took part in four group terms of the program, each lasting 3months. They were compared to a matched control group. Main outcome criterion was a reduction in the total score of the commitment to exercise scale (CES). In the completer analysis, we found statistically significant reductions in the CES total score over time (time×group; p=0.003) and significant improvements in overall eating psychopathology and quality of life (pre→post). The dropout rate was high (34%), mainly due to external reasons (time schedule, etc.). Findings point to specific effects of a newly developed outpatient sport therapy program for eating disorders. Detailed assessments of patients before assigning them to the program will be necessary to reduce dropout rates. The next step has to be a randomized controlled study.