Objective: In this study, we investigated the prevalence of glaucoma in patients with obstructive sleep apnea syndrome (OSAS). Material and Methods: Sixty-four patients with OSAS and 32 control subjects comprised the study group. Detailed ophthalmological examinations, computerized visual field analysis and imaging of the optic nerve head with Optical Coherence Tomography were performed. Diurnal intraocular pressure measurements were made on patients with OSAS. Patients with OSAS were divided into three groups (mild, moderate and severe) for severity of the disease based on their apnea-hypopnea indexes (AHI). Results: There was a statistically significant correlation among AHI, mean deviation and retinal nerve fiber layer thickness (p<0.05). Glaucoma was diagnosed in seven patients with OSAS (10.9%). One patient had primary open angle glaucoma and six patients had normal tension glaucoma. Five of the patients with glaucoma were in severe OSAS group. Conclusion: The results of this study show that OSAS is associated with glaucoma. Patients with OSAS should be followed regularly for glaucoma development and progression.