Increased numbers of circulating endothelial cells (CECs) have previously been reported after various diseases associated with endothelial injury. The aim of this study was to evaluate the CECs in patients with Behçet's disease and to demonstrate a possible association between CECs and disease activity. Sixty individuals (45 Behçet's disease patients and 15 healthy controls) with normal renal function are included in the study. Peripheral blood samples are first incubated with antiCD146 antibody and subsequently conjugated to immunomagnetic beads to isolate CECs. Cells are stained with UEA-1 before counting. Behçet's patients [7-135 cells/mL, mean 50 cells/mL, median 43 cells/mL (SD 35), P<0.001] have elevated numbers of CECs compared to controls [3-14 cells/mL, mean 9 cells/mL, median 8 cells/mL (SD 4)]. The number of CECs is higher in the active period of the disease compared to the inactive period. Further studies are needed to demonstrate the potential prognostic importance of CECs in Behçet's vasculitis.