Background: The retropalatal airway is one of the most collapsible sites during sleep in patients with obstructive sleep apnea (OSA). The primary anatomical contributors to increased collapsibility in the retropalatal segment remain unclear. Objectives: This study seeks to investigate how the balance between pharyngeal soft tissues and the bony enclosure influences retropalatal mechanical loads in patients with OSA. Methods: The segmental mechanical load of the retropalatal pharynx was determined by the region's critical closing pressure in 30 anesthetized, paralyzed and intubated subjects with OSA. The volumetric anatomical parameters of the retropalatal airway were evaluated using magnetic resonance imaging, and their associations with retropalatal closing pressures were analyzed. Results: Increased retropalatal closing pressure was associated with the increased proportion of volumetric pharyngeal soft tissues to the surrounding cervicomandibular bony frame (r = 0.791, p < 0.001), enlarged soft tissues of the lateral wall (r = 0.752, p < 0.001) and soft palate (r = 0.726, p < 0.001). The decreased volume of the nasopharynx (r = -0.650, p < 0.001) and pharyngeal cavity (r = -0.653, p < 0.001) indicated a relatively higher retropalatal closing pressure. The multivariate linear regression model demonstrated that the proportion of retropalatal soft tissues to the bony frame and volume of the soft palate predicted 69.4% of the variability in closing pressure (F = 30.674, p < 0.001). Conclusions: The increased volumetric proportion of pharyngeal soft tissue to the bone enclosure may be an important contributor to increased retropalatal mechanical loads. Copyright (C) 2011 S. Karger AG, Basel