Three-dimensional (3D) analysis of the deforming airway during tidal breathing has not been performed in children with obstructive sleep apnea. We used volume-gated magnetic resonance images to segment, surface, and volume mesh the airway of one child with obstructive sleep apnea syndrome (OSAS) and one control. A computational fluid dynamics (CFD) study was performed on each airway at flow rates corresponding to 10 time points of a respiratory cycle extracted from flow data averaged over 12 consecutive breathing cycles. 3D CFD analysis showed the minimum inspiratory pressure for the OSAS subject was -250.76 Pa and - 124.24 Pa for the control. Gated MRI images depicted an overall 47% decrease in airway volume over the inspiratory cycle for the OSAS subject while the control experienced no collapse. Pressure distribution corrected for nasal resistance and turbulence kinetic energy data suggest airway collapsibility in the OSAS is a function of pharyngeal resistance and fluid and tissue mechanics rather than entirely nasal resistance.