Obstructive sleep apnea (OSA) is a form of sleep disordered breathing with a high prevalence rate and OSA is associated with hypertension, coronary artery disease, stroke, peripheral vascular disease, heart failure and arrhythmias. The occurrence of stroke in patients with OSA is likely preceded by subclinical cerebrovascular disease, often termed “silent brain infarction” (SBI), which is detectable with brain magnetic resonance imaging (MRI). chronic nighttime hypoxemia and sleep disturbances in OSA patients may lead to elevated proinflammatory cytokines, markers of inflammation and plasma fibrinogen levels. This study was conducted to detect the occurance of silent cerebral infarction and measure the fibrinogen level in patients with obstructive sleep apnea syndrome (OSAS). This study was carried out in chest department in Benha University Hospital, it was conducted on 170 patients presented with OSA, Polysomnography, plasma fibrinogen level measurement and brain MRI were done for each patient.