 Obstructive sleep apnea OSA is a common disorder that is associated with substantial morbidity, including excessive daytime sleepiness, hypertension, and cardiovascular disease. Although Continuous Pressure Airway Pressure CPAP is effective treatment of objective and subjective complaints, adherence to CPAP therapy is suboptimal. Recently, pressure-relief CPAP C-flex,A-flex; Respironics; Murrysville, PA is available. The present study is single-blind,prospective, randomised, crossover study to compare the adherence and effects of therapy with C-flex, A-flex, and autoadjusting CPAP after 3 months of CPAP treatment. 