Sonography gives a characteristic picture of popliteal aneurysms, with an easily demonstrable connection of the sonolucent aneurysmal sac with the popliteal artery. It is a good screening procedure for suspected aneurysms and for patients with popliteal pain, mass or sudden distal ischemia. Three case reports of 5 popliteal aneurysms diagnosed by ultrasound are presented. A case of neurofibrosarcoma occurring in the popliteal fossa is shown for comparison.