Systematic cineradiographic observation of the upper airway with simultaneous polysomnography, termed somnofluoroscopy, was performed for a relatively large sample of obstructive sleep apnea patients. These observations suggest that (a) the site of upper airway occlusion may be oropharyngeal, hypopharyngeal, or both; (b) upper airway dynamics appear to be consistent within a given patient and variable among patients; and (c) a passive mechanism results in occlusion rather than active muscular contraction. Somnofluoroscopy is a relatively simple procedure that may be helpful in the selection of treatment for individual sleep apnea patients.