Previous reports of pulmonary function in patients with Morquio's disease have emphasized the restrictive nature of their ventilatory defect. We describe a patient in whom pulmonary disability was secondary to upper airway obstruction from collapse of the trachea during head flexion. The same phenomenon was demonstrated in one of two other patients with Morquio's disease, both of whom were asymptomatic. Positionally dependent airway obstruction may be an important cause of pulmonary disability in Morquio's disease.