The Klippel-Trenaunay syndrome (KTS) is a rare anomaly characterized by naevus, soft tissue hypertrophy and varicosities which is mainly unknown etiology. Associated deep venous system abnormalities have been reported with KTS. Here, a 4-year-old-boy with KTS was reported, because of the associated popliteal vein, common femoral vein with its deep and superficial branches, and external iliac vein agenesis. The originality of the presented case is that we have never observed such a case before.