Behçet's disease (BD) is a chronic systemic vasculitis characterized by recurrent oral and genital ulcers, uveitis, and skin lesions. It is also associated with an increased risk of developing thrombosis, although the prothrombotic mechanisms are not clearly defined. The role played by rheological alterations in the development of thrombotic events in BD is not well defined, existing little information on whether erythrocyte deformability (ED) may be involved in this issue. Therefore we aimed to evaluate ED by ektacytometric techniques in a large group of patients with BD in a non-active phase of the disease at sampling and in a well-matched control group, in order to establish a possible association between alterations in ED and the presence of thrombotic events. The patient group comprised 45 patients with BD (22 male, 23 female aged 42+/-14 years) and the control group comprised 46 healthy volunteers (23 male, 23 female aged 45+/-13 years). Twelve of the 45 patients with BD had a previous documented history of deep vein thrombosis at least six months before entering the study, and the other 33 did not. Erythrocyte elongation indexes (EI) at the three shear stresses tested (EI12, EI30, EI60) were not statistically different between patients and controls (EI12: P=0.453; EI30: P=0.411; EI60: P=0.403). There were no significant differences in these parameters, either, when patients with and without previous thrombotic events were compared (EI12: P=0.272; EI30: P=0.215; EI60: P=0.171). Our results suggest that ED is not compromised in BD and does not seem to be involved in the development of thrombotic events in these patients.