To explore the differences in upper airway morphology between positional (POSA) and non-positional (NPOSA) obstructive sleep apnea. Methods: This retrospective study enrolled 75 patients (45 NPOSA and 30 POSA) who underwent polysomnography (PSG) and computed tomography (CT). The differences in, and relationships of, the PSG values and CT data between POSA and NPOSA were analyzed. Results: Significant (p<0.05) differences between the two groups were found in the apnea/hypopnea index (AHI), lateral-AHI (L-AHI), soft palate length (SPL), cross-sectional palatopharyngeal area, and the coronal diameter (CD) of the palatopharyngeal area at the narrowest part of the glossopharynx, which were all higher in POSA, except for SPL, AHI, and L-AHI. L-AHI was correlated with the cross-sectional area (r=-0.306, p=0.008) and CD (r=-0.398, p<0.001) of the palatopharyngeal area, the cross-sectional area (r=-0.241, p=0.038) and CD (r=-0.297, p=0.010) of the narrowest level of the glossopharynx, the CD of the glossopharynx (r=-0.284, p=0.013), body mass index (BMI, r=0.273, p=0.018), SPL (r=0.284, p=0.014), and vallecula-tip of tongue (r=0.250, p=0.030). The SPL and CD at the narrowest part of the glossopharynx were included in the simplified screening model. Conclusions: In NPOSA, the CD of the upper airway was smaller, and the soft palate was longer, than in POSA. These differences may play significant roles in explaining the main differences between NPOSA and POSA.