INTRODUCTION: Obstructive Sleep Apnea Syndrome (OSAS) is a prevalent condition associated with numerous adverse health consequences. Exercise therapy was described as a valuable OSAS treatment alternative to continuous positive airway pressure. OBJECTIVE: The objective of the present systematic review was to assess the efficacy of exercise in reducing OSAS severity and associated comorbidities. SETTING: We queried MEDLINE and SCOPUS and ScienceDirect databases with the following keywords: "sleep apnea" and "sleep disordered breathing" for the population and "physical activity", "fitness" and "exercise" for the intervention. RESULTS: Eight studies including a total number of 354 patients showed that OSAS severity was significantly reduced after intervention. This reduction was associated with significant improvement in cardio-vascular fitness, sleep quality and quality of life. Conversely, this effect was not directly related to body weight reduction. CONCLUSION: This systematic review suggests that physical activity should be recommended as a treatment for OSAS patients. However, further research is necessary to demonstrate this long-term efficiency with a higher level of confidence and to better understand the underlying physiological mechanisms.