This study was carried out to test the hypothesis that changes in head/body position induce changes in upper-airway dimensions. Contiguous images were obtained by means of magnetic resonance imaging in normal awake subjects during nasal breathing. A statistical analysis was made on 5 consecutive slices, including the most constricted sites in both the retropalatal and retroglossal regions. Dimensional changes in the upper airway in association with changes in head/body position were evaluated. In the retropalatal region, there was a significant decrease in the lateral dimension in the lateral recumbent position compared with that in the supine position. The cross-sectional area in the retroglossal region was significantly increased in both the "supine with the head rotated" and "lateral recumbent" positions. This change was accompanied by significant volumetric changes in the retroglossal region. Thus, sleeping with the head rotated may be effective for improving upper-airway obstruction.