Conclusions: This study has shown that the body mass index (BMI), neck circumference, and modified Mallanpati grade (MMP) are predictive of severity of obstructive sleep apnea/hypopnea syndrome (OSAHS). The neck circumference and MMP were revealed to be important morphological features in the responders whose apnea/hyoponea index (AHI) was substantially decreased by positioning during sleep. Objective: The aim of this study was to assess the predictive power of routine physical examination of the upper airway by an otorhinolaryngologist to identify OSAHS in Chinese patients, and to clarify the interaction of lateral and supine sleeping positions with upper airway morphology in patients with OSAHS. Methods: In all, 103 consecutive patients with OSAHS (48 men and 65 women) underwent polysomnography and upper airway morphological examination. Upper airway morphology and anthropometric variables were evaluated to determine different severity of OSAHS in the responders and nonresponders. Results: The neck circumference, BMI, and MMP showed statistical correlations with AHI and decreased AHI for changed sleeping position. Multiple logistic regression analysis showed that the neck circumference and MMP were significant predictors for the responders (p = 0.023, odds ratio = 1.180 and p = 0.006, odds ratio = 1.922, respectively).