Here we describe a case of a 19-year-old young man with acute pulmonary embolism and left lower leg thrombosis after lower limb trauma post thrombolytic therapy and persistent D-Dimer elevation. Radionuclide venography revealed deep venous thrombosis in the left infra-popliteal to iliofemoral veins with good collaterals. Lower extremity ultrasound showed thrombosis over the left iliofemoral vein and downstream veins. We found that the left greater saphenous vein was an alternative pathway of collateral systems in the presence of deep vein thrombosis at the infra-popliteal vein.