Craniofacial anomalies are recognized causes of obstructive sleep apnea syndrome (OSAS) in children. Current literature is limited due to rarity of cases. Furthermore, the mechanism of upper airway obstruction is not clearly understood. We would like to report a family (father and 2 sons) who are suffering from Crouzon's syndrome. The two brothers (ages 1 and 3) were found to have significant obstructive sleep apnea syndrome (OSAS) with failure to thrive. Nasal continuous positive airway pressure (CPAP) markedly improved their OSAS and resulted in accelerated weight gain. The nasoendoscopy and magnetic resonance imaging (MRI) scan taken during natural sleep showed that choanal stenosis, maxillary hypoplasia, posteriorly displaced tongue, lengthened soft palate and adenoid tissues were important in the pathogenesis of upper airways obstruction in Crouzon's syndrome. Nasal CPAP improved airway obstruction by opening a narrow slit as demonstrated by MRI. Our results suggest that OSAS occurred in children with Crouzon's syndrome and that nasal CPAP was a useful treatment modality.