Oral apthous ulcers and skin lesions are the primary symptoms of Behcet's disease (BD). To date, there is no study to investigate possible associations between these lesions and endothelial functions. We have hypothesized that active BD period with oral and skin lesions might have more deteriorating effect on endothelial functions. Thirty-five patients with BD were registered for the study. Each subject was evaluated two times in both active and inactive disease periods. The subject with at least 30 days of lesion-free period was regarded in the inactive disease period, and the subject with any oral and/or skin lesions was regarded in the active disease period. For the control group, 35 healthy age- and sex-matched subjects were registered. In each subject, flow-mediated dilation (FMD) of the brachial artery after transient ischemia was evaluated in both active and inactive disease periods. High-sensitivity C-reactive protein (hsCRP) values (3.30 +/- 5.76 vs 14.19 +/- 13.55 vs 1.82 +/- 1.31, P<0.001) and FMD values (13.89 +/- 5.57 vs 8.53 +/- 4.78 vs 15.83 +/- 5.29, P<0.001) were significantly different among the BD patients in inactive and active disease periods and among control subjects. FMD values in inactive and active disease periods modestly correlated to hsCRP and low-density lipoprotein cholesterol values. Brachial FMD is more prominently impaired in BD patients within the active disease period. BD patients are possibly more vulnerable to cardiovascular manifestations when they are in the active disease period.