Angiography of a 53-year-old male suffering from intermittent claudication demonstrated no abnormal finding. US with a 7.5MHZ transducer at the popliteal fossa showed a hypoechoic fusiform area in contact with the left popliteal artery posteriorly. Enhanced CT showed a curvilinear cystic change along the wall of the left popliteal artery posteriorly. A popliteal adventitial cyst was diagnosed preoperatively and confirmed at the time of surgery.