Adherence to CPAP is and will remain the touchstone for patients with obstructive sleep apnea syndrome. The authors try to clarify the many difficulties encountered regarding this matter, its epidemiological implications, factors predicting non-adherence to treatment, and which are the most effective ways to alleviate it. Therefore a practitioner can increase the degree of adherence and he can decisively influence the favourable effect of this type of therapy on a short-term as well as long-term basis.