Many anatomical factors are known to cause obstructive sleep apnea syndrome (OSAS), but only few studies have examined the relationship between the morphology of pterygoid hamulus (PH), upper airway, and OSAS severity. This study aimed to investigate the relationship between the severity of OSAS and PH morphology and other anatomical variations of the upper airway. The data of the patients who underwent polysomnography and diagnosed with OSAS were retrospectively reviewed, and those who underwent paranasal sinus computed tomography were determined. The patients were divided into three groups according to the apnea–hypopnea index (AHI) scores obtained from the polysomnography (mild, moderate, and severe). The relationship between PH thickness, length and interpterygoid distance, and the severity of AHI was investigated. Seventy-four patients were included in the study. In patients with severe OSAS (1.83 ± 0.29 mm), the PH bone thickness was significantly thicker compared to those with mild OSAS (1.59 ± 0.36 mm) (p = 0.03). When the interpterygoid distance and its ratio to the velopharyngeal length were examined, it was found significantly shorter in patients with severe OSAS than mild cases (p