Brachial artery endothelial dysfunction was shown previously in a small group of Behçet's disease (BD) patients. This study aimed to compare the endothelial function in BD patients with and without vascular involvement. The study group consisted of 25 BD patients with vascular involvement, 25 BD patients without any vascular disease and 46 healthy controls. Brachial artery flow-mediated (endothelium-dependent) dilation (FMD), nitroglycerine-induced dilation and carotid artery intima-media thickness were measured. FMD was impaired in patients with BD (10.41 +/- 3.85%) compared to healthy controls (14.41 +/- 3.39%, p < 0.001). FMD was significantly lower in BD patients with vascular involvement (8.80 +/- 3.63%) than those without any vascular disease (12.02 +/- 3.43%, p = 0.003). This study reveals that endothelial dysfunction documented by brachial artery FMD is a feature of BD, and it is more prominent in patients with vascular involvement.