Although the duplication of the inferior vena cava (IVCD) is usually clinically silent and often detected incidentally by image analysis, it may have important relevance during retroperitoneal surgery and endovenous procedures. Furthermore, IVCD may represent the primary provocating factor of unilateral iliofemoral vein thrombosis in patient with hypoplasia or thrombosis of one of the caval veins. This was the case in a 37-year-old man with acute painful swelling of the right leg. The patient was treated successfully by endovenous reconstruction of the occluded caval vein. A review of the pathophysiology, clinical manifestation and treatment of the IVCD is provided here.