What benefit of physical activity in tertiary prevention? In tertiary prevention, regular physical activity associated with the reduction of sedentary behaviors reduce the risks of recurrence or aggravation of the disease, decrease co-morbidities, increase physical capacities and improve quality of life. These effects are found with a high level of evidence in chronic diseases as various as cardiovascular diseases, type 2 diabetes, cancers, COPD, osteo-articular diseases, anxio-depressive disorders. The scientific evidence of physical activity as a non medicamentous treatment of chronic diseases is not any more to make. However the level of physical-activity of the subjects carrying chronic diseases is very low, well below the recommendations and their time of sedentariness remains too h. It remains to determine the effective minimal amount of physical activity, how to replace time of sedentariness by time of physical-activity, and especially how to maintain the physical-activity on the long run.