Marfan's syndrome is a hereditary disorder characterized by a defect in connective tissue, resulting in tissue laxity. It is associated with a high prevalence of obstructive sleep apnea (OSA). The aim of this study was to determine whether excessive upper airway collapsibility during sleep is an important pathophysiologic factor predisposing these individuals to OSA. We measured upper airway closing pressures (UACP) during sleep in 12 patients with Marfan's syndrome and 6 age-, and height-, and weight-matched control subjects. Ten of the patients had OSA, defined as an apnea/hypopnea index > 5. All patients with Marfan's syndrome, including the two patients without OSA, demonstrated increased upper airway collapsibility during sleep, with a mean UACP of -2.5 +/- 0.5 cm H2O during slow-wave sleep (SWS). In contrast, only two control subjects demonstrated upper airway closure. However, this was at significantly higher suction pressures, with a mean UACP of -5.6 +/- 0.4 cm H2O during SWS (p < 0.005). These data suggest that patients with Marfan's syndrome have abnormally increased upper airway collapsibility during sleep. It is possible that this is related to the characteristic connective tissue defect of this disorder.