Cystic adventitial disease (CAD) is a rare cause of claudication. We report a case of CAD involving the external iliac artery, with possible cyst rupture intramurally causing significant long segment stenosis of the external iliac artery.A 52-year-old female presented with sudden onset (over 1 day) lifestyle-limiting claudication affecting the left calf and thigh. CT angiography of the lower limbs revealed an eccentric low density wall thickening of the left external iliac artery (EIA) producing a 70% stenosis and a cystic lesion just distal to the stenosis.A diagnosis of cystic adventitial disease was made and the patient proceeded to iliofemoral bypass.