It is widely accepted that the size of the airway and the level of upper airway muscle activity contribute to the pathogenesis of obstructive sleep apnea (OSA). However, some individuals with normal airway size and apparently normal upper airway muscle activity nonetheless develop OSA. Recent data and analysis suggest that airway shape may also contribute to the development of OSA; patients with OSA tend to have elliptical airways, with the long axis of the ellipse oriented along the anteroposterior axis, and this orientation may adversely affect upper airway muscle function. By incorporating airway shape, airway size, and upper airway muscle activity into a unified hypothesis of the pathogenesis of OSA, it may be possible to reconcile discrepant anatomic and electromyographic findings in patients with OSA, to explain the difficulty of selecting appropriate surgical therapy for patients with OSA using currently available diagnostic tools, and to understand the often disappointing response to upper airway surgery in these patients.