Cystic adventitial disease of blood vessels is a rare condition, more so when veins are involved. We report the case of a 36-year-old man who was referred to us after an intraoperative diagnosis of a left common femoral vein mass. This patient, who had a history of deep vein thrombosis and pulmonary embolism, had presented to an outside facility with recurrent left lower extremity pain and swelling. At our hospital, he underwent excision of the vein mass with interposition vein grafting using the left internal jugular vein. In this report, we discuss the presentation, diagnosis, treatment, and pathology of this rare condition.