Abstract: Introduction: Large vessel involvement is one of the hallmarks of Behcet's disease (BD). Like the other manifestations of the disease, its prevalence differs due to ethnic variation and environmental factors. The aim of this study is to find the characteristics of vasculo Behcet in Iran. Materials & Methods: In a cohort of 4429 patients with BD, those with vascular involvement were selected (VB). Different manifestations of the disease were compared with the remaining group of BD patients by chi square test. A confidence interval at 95% (CI) was calculated for each item. Results: Vascular involvement was seen in 377 cases (8.5%, CI:0.8). Venous involvement was seen in 367 cases: Deep vein thrombosis in 272 (6.1%, CI:0.7), superficial phlebitis in 99 (2.2%, CI:0.4), and large vein thrombosis in 40 (0.9%, CI:0.3). Arterial involvement was seen in 24 casess (21 aneurysms and 3 thrombosis). Twelve patients showed both arterial and venous involvement. The mean age of the patients with VB was slightly higher (27.2 vs. 25.9, p<0.02), but the disease duration was significantly longer in them (10.1±7.3 vs. 8.9±6.8, p<0.002). VB was more common in men (p<0.000001). As the presenting sign, ocular lesions was less seen in VB (p<0.002). VB was associated with a higher frequency of genital ulcers (p<0.00006), skin lesions (p<0.000001), joint involvement (p<0.000001), epididymitis (p<0.000001), neurologic (p<0.00004) and G.I. involvement (p<0.005). The juvenile form was lower in VB (p<0.007). The frequency of false positive VDRL, pathergy. HLAB5 or HLAB27 showed no significant difference between two groups. Conclusion: In Iranian patients with BD, large vessel involvement is not common. It may be sex related, and is more common in well-stablished disease (with multiple organ involvement and longer disease duration). No relationship seems to exist between vascular involvement and false positive VDRL, pathergy phenomenon and HLAB5 in BD.