Objective: To evaluate the clinical characteristics of patients with positional obstructive sleep apnea hypopnea syndrome (P-OSAHS). Methods: The study retrospectively analyzed 171 men diagnosed as having OSAHS in Beijing Tongren Hospital, Capital Medical University, during July 2012 to June 2014. That the apnea hypopnea index (AHI) during supine position of ≥ 2 times by the AHI during lateral position was employed as the standard for P-OSAHS. Subjective symptoms, physical examinations, polysomnography (PSG), and three-dimensional computer tomography (3-D CT) were compared between P-OSAHS group and control group with non-positional OSAHS. Results: Of 171 patients with OSAHS, 47(27.5%) had P-OSAHS and 124 (72.5%) presented with non-positional OSAHS. There were significant differences between two groups in BMI, neck circumference, AHI, the lowest oxygen saturation, the percentage of time with oxygen saturation below 90% (CT90), and the minimal anterior-posterior airway dimension of the glossopharynx (P<0.05). The AHI was the only predictive parameter for P-OSAHS (P<0.01). There were significant differences in the incidence of P-OSAHS between patient with mild or moderate disease (AHI<30), severe disease (AHI≥30 but<60), and extremely severe disease (AHI≥60) (81.8% (18/22) vs 45.3% (24/53) vs 5.2% (5/96), P<0.05). Conclusion: The severity of OSAHS closely related to the incidence of P-OSAHS, with significant differentce in the incidence of P-OSAHS between the patients with different severity of OSAHS.