The purpose of the present study was to test endothelial function and to determine if plasma homocysteine levels are associated with endothelial injury in patients with Behcet's disease (BD). Flow-mediated dilation in patients with BD was smaller than that of control subjects (p = 0.001), and mean plasma homocysteine levels in patients with BD were significantly higher (p = 0.0001). On regression analysis, only mean plasma homocysteine concentration was independently related to flow-mediated dilation (F = 5.7, p = 0.001).