Aneurysms of the iliac veins are extremely rare. We report a case of a 51-year-old male who was admitted for swelling of the lower right limb. Sonography and ascending phlebogram showed a complete occlusion of the right femoropopliteal veins, both iliacs and the inferior vena cava (IVC). A large collateral circulation throughout the paravertebral plexus and azygos system was also observed. The CT scan revealed a 5 x 9 cm thrombosed aneurysm of the right external iliac vein and a congenital hypoplasia of the infrarenal IVC. Anticoagulant treatment and compression with elastic stocking was started. The 3-month follow-up showed mild residual edema of the right lower limb. The literature on this pathology is extensively reviewed.