Simple ganglions are most common benign tumor of the hand and wrist. However, cystic adventitial disease is an uncommon vascular anomaly first described in 1947 in the external iliac artery. It usually involves the popliteal artery, although other arteries and veins may also be involved. Radial artery adventitial cysts are found directly within the adventitia, whereas the more common wrist ganglions may extrinsically compress or adhere to the artery walls. The diagnosis is rarely made before surgery because of their similar appearance and location. The authors report a rare case of a 46-year old woman with mucoid adventitial cyst of the radial artery in the wrist.