Ten patients with autonomic nervous system dysfunction (familial dysautonomia, juvenile diabetes, or Shy-Drager syndrome) were studied to assess the impact of their impairment on breathing during sleep. Several types of breathing dysfunction during sleep were identified independent of the patients' primary complaints. Obstructive sleep apnea syndrome was the most common; central sleep apnea and disturbances of te respiratory oscillator also were seen. Esophageal reflux was found to be the cause of some sleep-related problems. The observed respiratory irregularities were not associated with the usual cardiac response; a "decoupling" of heart rate from the respiratory cycle was noted during sleep in these patients.