The prevalence of peripheral artery disease (PAD) has been increasing in parallel with the increasing prevalence of the atherosclerotic disease. Therefore, we have to be familiar with the diagnostic approach used for ischemic symptoms in the lower limbs. Adventitial cystic disease (ACD) is rare but not negligible as one of the differential diagnoses of intermittent claudication (IC). Although duplex ultrasound and magnetic resonance imaging (MRI) are helpful tools for the diagnosis of ACD, further imaging modality is needed to avoid misdiagnosis. A 64-year-old man with a mitral valve prosthesis presented to our hospital with a one-month history of IC in the right calf after walking for approximately 50 meters. On physical examination, the pulse in the right popliteal artery was not palpable, nor were the dorsal pedis artery and posterior tibial artery, although there were no other symptoms of ischemia. His right ankle-brachial index (ABI) was 1.12 at rest but decreased to 0.50 after exercise. Three-dimensional computed tomography (CT) angiography revealed a severe stenotic lesion approximately 70 mm long in the right popliteal artery. Therefore, we diagnosed PAD in the right lower limb and planned endovascular therapy. The stenotic lesion was markedly reduced on catheter angiography when compared with CT angiography. However, intravascular ultrasound (IVUS) detected little atherosclerosis and cystic lesions within the wall in the right popliteal artery that did not involve the arterial lumen. Especially, IVUS clearly demonstrated that the crescent-shaped cyst compressed the arterial lumen eccentrically and other cysts surrounded the lumen circumferentially like petals. Because IVUS revealed these cysts to be extravascular structures, the patient was subsequently thought to have ACD of the right popliteal artery. Fortunately, his cysts reduced in size spontaneously and his symptoms disappeared. We have monitored the patient's symptoms, ABI, and findings on duplex ultrasound for seven years, during which there has been no recurrence. In this case, we diagnosed ACD in the popliteal artery by IVUS rather than duplex ultrasound and MRI.