There are growing evidences suggesting endothelial dysfunction is associated with cardiovascular events and cerebrovascular events. The physiological role of endothelium is relevant to vascular homeostasis through maintenance of vascular tone, balancing blood fluidity and thrombosis, and control of the vascular inflammatory process. To do these function, endothelium produce various substances such as nitric oxide (NO), endothelin, tissue plasminogen activator and adhesion molecules, etc. Flow mediate dilation (FMD) of brachial artery can measure the status of endothelial function of systemic conduit artery. FMD is mediated through endothelial NO. So it represents a bioavailability of NO of vascular endothelium. FMD can predict risk and prognosis of cardiovascular disease in patients with coronary artery disease. Also it is associated with cerebral small vessel disease. Endothelial dysfunction is a reversible disorder which can be improved by modifying vascular risk factors including hypertension, diabetes mellitus, hyperlipidemia, cessation of smoking and exercise. The alternation of endothelial function can be measured with FMD. FMD is a reliable surrogate marker of endothelial function and can be used as a prognostic factor in patients with vascular disease. Journal of Neurosonology 1(1):29-34, 2009

Key Words: Endothelial function, Flow mediate dilation, Stroke