We report a case of Behçet's disease complicated with a popliteal aneurysm, which appeared 8 years after first etiologic diagnosis. The points of interest of this observation are the pre-operative explorations and particularly the Magnetic Resonance Angiography (RMA). This last seems to be particularly safe for aortic and lower limbs aneurysms explorations, and can be performed without arterial functions. In fact the risk of arteriogram is effective in Behçet's disease with secondary false aneurysms. RMA and US-Doppler scan must be first proposed in Behçet's disease in case of aortic and peripheral aneurysms.