Vein aneurysm is a rare encountered lesion. We describe a case of extensive bilateral iliac vein aneurysm as an accidental finding during abdominal ultrasonography of a 39-year-old male marathon runner. Common iliac vein dimensions were respectively: right 39 x 42 x 60 mm and left 43 x 55 x 73 mm, with no signs of thrombosis or spontaneous echocontrast; mean flow velocity was 0.10 m/s with normal dynamics of venous flow. Furthermore we observed abnormal dilatation of the cava vein as well as the common femoral and popliteal veins. Other venous districts, detectable by color-Doppler ultrasound were normal. Known congenital or acquired conditions predisposing to aneurysm and/or ectasia were not detected.