The purpose of this study was to evaluate factors associated with nightly variability in sleep-disordered breathing. In this study, variability in sleep-disordered breathing over two consecutive laboratory nights was evaluated in 71 aged volunteers with varying levels of sleep apnea. High variability (n = 13) and low variability (n = 58) groups were formed on the basis of an absolute two-night apnea/hypopnea index difference of a minimum ten events per hour. Results indicate high variability was related to longer soft palate measurements and the presence of nasal obstruction on physical examination. Within the high variability group, variation in sleep-disordered breathing occurred within identical gross body position over the two nights. The results suggest that local, anatomic factors affecting airway patency may not be constant from night to night.