This document discusses obstructive sleep apnea syndrome (OSAS). It defines OSAS and describes the stages of sleep. OSAS is characterized by pauses in breathing or instances of reduced breathing during sleep. The severity is determined by the apnea-hypopnea index. Symptoms include daytime sleepiness and snoring. Risk factors include obesity, large tongue, and nasal obstruction. Treatment involves weight loss, sleep positioning, continuous positive airway pressure devices, and sometimes surgery to improve breathing during sleep. Complications of untreated OSAS include high blood pressure, heart disease, and stroke.