Deep venous thrombosis (DVT) tops the differential diagnosis list for unilateral lower extremity edema, but another entity could imitate or even cause a DVT. May-Thurner syndrome is caused by compression of the left common iliac vein by the overlying right iliac artery, resulting in impeded venous blood flow from the left lower extremity. The left leg becomes edematous, causing discomfort and concern. Early recognition of May-Thurner could prevent a DVT and provide symptomatic relief.