Duplex sonography and angiography revealed cystic adventitial degeneration (CAD) in a 45-year-old patient with intermittent claudication of the right calf and an initial maximum walking distance of 50 m. Intraoperatively we found a cystic lesion containing gelatinous fluid in the adventitial layer of the popliteal artery. Because of the extended lesion, resection of the involved segment was performed, followed by autologous venous reconstruction. CAD is a rare disease and should be considered in young patients without systemic atherosclerosis. The surgical treatment is, depending on the case, either nonresectional by circumferential removal of adventitial cysts or resectional followed by autologous reconstruction in extended lesions or total occlusion of the artery.