Objective: The aim of this prospective study is to compare middle ear pressures between adult patients with obstructive sleep apnea syndrome (OSAS) who have no Eustachian dysfunction and healthy controls.Methodology: Eighty-nine patients presented to Otolaryngology and Chest Disease Departments with snoring and gasping of breath during sleep were included to the study.Diagnosis was based on "witnessed sleep apnea" criterion.Eighty-nine volunteers without complaints of sleep apnea were employed as control group.Exclusion criteria: Patients on continuous positive airway pressure (CPAP) and bi-level positive airway pressure (BPAP) as well as those with history of previous ear surgery, those with primary middle ear disorders such as acute, chronic or adhesive otitis, those with mechanic obstruction such as Eustachian tube dysfunction, septum deviation, adenoid vegetations, nasal polyposis and nasal synechia, those with nasal obstruction caused by inflammatory or allergic factors, those with nasopharynx mass or inflammation were excluded.Same criteria were used for exclusion in control group.In order to achieve standardization, tympanometric measurements were performed on the second 45 after last gulp.Results of patients with OSAS were compared to those in control group.