Neurologists are becoming increasingly aware of the frequency and clinical importance of sleep-related respiratory impairment. Sleep-induced narrowing of the upper airways underlies the widespread and supposedly trivial complaint of snoring, which may not only constitute a risk factor for the cardiocirculatory system, but in predisposed individuals, may lead to a sleep apnea syndrome, with its array of serious disturbances, including hypersomnia, systemic and pulmonary hypertension and ultimately heart failure. Idiopathic chronic alveolar hypoventilation, or Ondine's curse, is a fairly stereotyped clinical syndrome: sleep-related respiratory insufficiency in the absence of airways stenosis. Finally, sleep, and REM sleep in particular, significantly aggravates hypoventilation in patients with chronic obstructive pulmonary disease (COPD), kyphoscoliosis or chest musculoskeletal disorders.