BACKGROUND: Obstructive sleep apnea (OSA) has been reported to increase risk of ischemic stroke. This study was performed to investigate the prevalence and relationship of subclinical white matter damages (SD) in patients with OSA. METHODS: All subjects (n = 54) had brain MRI and nocturnal polysomnogram (PSG). SD are defined by nonsymptomatic lacunar infarcts > 3 mm or periventricular white matter changes (PVWC). We analyzed the difference between OSA patients with and without SD (SD and non-SD groups), and also with and without PVWC. Using apnea-hypopnea index (AHI), we classified OSA into mild (5< or =AHI< or =15) and moderate to severe (AHI>15). RESULTS: SD group (n = 31) showed significantly increased apnea-hypopnea index (AHI), apnea index (AI) and oxygen desaturation index (ODI) compared to non-SD (n = 23). Among the 37 patients without lacunar infarctions, 14 showed PVWC while the other 23 did not have any lesions. Compared to non-SD group, SD group showed increased AHI and ODI, and decreased lowest SaO2 (p < 0.05). Similarly, AHI and ODI were higher and the lowest SaO2 was lower in patients with PVWC than without PVWC (p < 0.05). Moderate to severe OSA group showed more frequent subclinical or periventricular white matter changes than mild group (p < 0.05). CONCLUSIONS: Severity of OSA showed a positive correlation with the occurrence of subclinical white matter damages. OSA may cause subclinical white matter damages.