Objectives: We investigated the prevalence of silent cerebro-vascular lesions and atrophy in patients with obstructive sleep apnea syndrome (OSAS) and the correlation between OSAS severity and prevalence of silent cerebrovascular lesions in Turkish patients. Methods: Study subjects were 56.35 OSAS, polysomnography (PSG)-confirmed patients who visited the sleep disorders clinic in our university hospital. None had a history of cerebrovascular disease (CVD). The control group consisted of normal subjects who had no history of snorring, apnea, excessive daytime sleepiness and had under 10 score of epworth sleepiness score. We performed a cross-sectional study on OSAS severity and the prevalence of silent cerebrovascular lesions and atrophy detected by brain MRI analysis. Results: The control group included 21 subjects, the moderate OSAS (AHI 15 to < 30/h) group included 7 patients with a mean AHI of 22.0 +/- 5.3/h while the severe OSAS (AHI >= 30/h) group included 28 patients with a mean AHI of 60.0 +/- 27.4/h. A larger percentage of patients with severe OSAS had a higher BMI than those with moderate OSAS and control subjects (P < 0.05). Silent ischemic gliotic lesions was identified in 10 (38.2%) control subjects, 27 (61.8%) with moderate and severe OSAS. Among control subjects and the moderate, and severe OSA groups, 10 (38.2%), 6 (85.7%) and 21 (77.7%) respectively, had periventricular hyperintensity (PVH); most PVH was mild to moderate. Conclusion: Results indicate that patients with moderate to severe (AHI >= 15/h) OSAS have a higher prevalence of silent cerebrovascular lesion than those with no OSAS.