May-Thurner syndrome is caused by left iliac vein compression by the overlying right common iliac artery. The patient is typically a young female (second to fourth decade) presenting with left ilio-femoral deep vein thrombosis(DVT). The presence of a spur, possibly from injury to the vein endothelium from the arterial pulsations, predisposes to the development of DVT and differentiates this condition from bland DVT.