Adventitial cystic disease or degeneration of the blood vessel wall is an unusual form of peripheral vascular disease that occurs almost exclusively in the popliteal artery and accounts for an estimated one in 1200 cases of claudication. The cause of adventitial cystic disease is unknown, but it has been attributed to repeated trauma, an ectopic ganglion, or primary dysplasia of the vascular connective tissue. We describe an unusual case of adventitial cystic disease of the lesser saphenous vein located adjacent to the ankle joint. Only a handful of cases of venous adventitial cystic disease have been reported in the English literature, and, to our knowledge, none involved the lesser saphenous vein.