The Sleep Apnea Syndrome consists of sleep-induced disturbances of breathing and breathing-induced disturbances of sleep. Symptoms of pathologic sleepiness and, less commonly, frequent awakenings and light sleep reflect the fragmentation of sleep by repeated respiration-related arousals. Snoring, intermittent choking, and nocturnal dyspnea reflect varying degrees of upper airway obstruction associated with Sleep Apnea Syndrome. Observations of breathing during sleep show varying combinations and degrees of periodic breathing, apneas, and hypoxemia. In more severe cases, cardiovascular complications, including systemic and pulmonary hypertension and cardiac arrhythmias, occur. The clinical spectrum thus varies from the asymptomatic patient, to one with chronic cardiac and respiratory failure who is at risk of sudden death. Most patients are disabled by varying degrees of pathologic sleepiness.