Obesity is a well-known cause of upper airway narrowing, respiratory failure and resulting hypoxemia and hypercapnia, and cardiac arrhythmias during sleep. Obese patients are prone to snore loudly and to develop obstructive sleep apnea syndrome and also obesity-hypoventilation syndrome. Repeated nocturnal upper airway obstruction may cause respiratory failure and cor pulmonale and frequent awakenings, and result in nocturnal choking, with daytime drowsiness, somnolence and irritability. The purpose of this article is to review the evidence for these accepted facts and to consider a variety of new information that relates to the pathogenesis, symptomatology and treatment of sleep disorders caused by obesity.