Objectives: This study aimed to investigate the eustachian tube dysfunction (ETD) of patients with obstructive sleep apnea syndrome (OSAS) using the Eustachian Tube Dysfunction Questionnaire-7 (ETDQ-7). Patients and Methods: The study included 96 patients (78 males, 18 females; mean age 39.4±12.2 years; range 18 to 64 years) diagnosed with OSAS by polysomnographic evaluation. All patients were administered the ETDQ-7. Age, sex, presence of septum deviation, Epworth Sleepiness Scale, apnea-hypopnea index (AHI), lowest oxygen saturation, and oxygen desaturation index parameters were recorded. The patients were divided into mild, moderate, and severe OSAS groups according to the AHI score. The parameters of the cases in each group were compared, and their correlation with the ETDQ-7 scores was evaluated. Results: The fourth question score and the total score in the group with severe OSAS were significantly higher than the groups with mild and moderate OSAS (p<0.05 for all). The fourth question score and the total score were significantly higher in the group with moderate OSAS than the group with mild OSAS (p<0.05 for all). There was a significant positive correlation between the oxygen desaturation index and the scores of questions 1, 3, 4, 6, and 7 and the total score (p<0.05 for all). Conclusion: Questionnaire scores were higher in patients with severe OSAS compared to mild to moderate OSAS patients. Based on this data, we would like to emphasize that OSAS cases may develop ETD and other related pathologies.