Some specific morphological differences between obstructive sleep apnea (OSA) and non-OSA persons account for mechanisms for development of pharyngeal airway obstruction during sleep. The pharyngeal airway is analogous to a collapsible tube within a rigid box which can demonstrate three key mechanisms of pharyngeal closure: increase of respiratory efforts during OSA; increase of tissue pressure surrounding the pharynx caused upper airway anatomical imbalance by the excessive amount of soft tissue (obesity) and small maxillomandibular enclosure; reduction of longitudinal tension of the pharyngeal airway particularly in central obese patients with reduced lung volume. Contribution of craniofacial abnormalities to OSA differs among the countries and races with larger influence in the Asian people. The anatomical imbalance can be detected by lower hyoid bone in the lateral cephalogram. There are, however, OSA mechanisms unexplained by the simple collapsible tube model. For example, mechanical disadvantage of fat deposition at the tongue base, mechanical interaction between the tongue base and soft palate through the gravitational impact on the soft tissue, valve-like behavior of the soft palate and epiglottis, and surface tension of pharyngeal airway mucosa. Clearly, it is necessary to develop a more comprehensive clinically useful morphological model in understanding the OSA pathophysiology.