Objective: To determine the influence of altered head or tongue posture on upper airway (UA) volumes using MRI imaging based on a new objective and validated UA evaluation protocol. Setting and sample population: One supine CBCT and five sagittal MRI scans were obtained from ten subjects in different head and tongue positions: (a) supine neutral head position (NHP) with the tongue in a natural resting position with the tip of the tongue in contact with the lingual aspect of the lower incisors (TRP); (b) head extension with TRP; (c) head flexion with TRP; (d) NHP with the tip of the tongue in contact with the posterior edge of the hard palate (THP); and (e) NHP with the tip of the tongue in contact with the floor of the mouth in contact with the caruncula sublingualis. Material and methods: Based on a validated CBCT UA analysis, the retropalatal, oropharyngeal and the corresponding total volumes were measured from each MRI scan. Wilcoxon signed-rank test was applied to determine the statistically significant difference in mean volume between the baseline head and tongue posture (NHP with TRP) and the other postures. Results: Five females and five males with a mean age of 46.5 ± 13.7 years volunteered for this pilot study. UA volumes, particularly the oropharyngeal volume, increased significantly with head extension and NHP with THP and decreased significantly with head flexion. Conclusion: Altered head and tongue posture proved to affect UA volumes, thus representing confounding variables during three-dimensional radiographic image acquisition.