Cystic adventitial disease (CAD) is a rare vascular disorder predominantly seen in adults without cardiovascular risk factors. We report a case of CAD involving the common femoral vein in a 38-year-old female presented with right lower extremity swelling that was initially misdiagnosed as deep vein thrombosis (DVT). A computed tomography revealed a cystic structure that compressed the right common femoral vein with resultant severe stenosis of the vascular lumen. Complete evacuation of the cyst with excision of the cyst wall was performed, and the patient remained symptom-free at 3 year follow-up. This case highlighted that the rare venous CAD should be incorporated in the differential diagnosis of unilateral lower extremity swelling suspicious for a DVT. Complete evacuation and surgical excision of the cyst often conferred favorable clinical outcome.