The use of fibular free flaps has become established as a reliable and popular method for reconstruction of segmental mandibular defects. Preoperative determination of adequate perfusion to the donor extremity is necessary to assure lower extremity viability after flap harvest. Vascular variations and peripheral arterial occlusive disease may exist whereby sacrifice of peroneal vessels can cause ischemia to the lower leg and foot. The purpose of this study was to evaluate the usefulness of CT angiography in the patients who need fibular free flaps. In 101 consecutive patients, clinically judged to be satisfactory candidates for fibula free transfer, CT angiography were studied. Vessels were assessed for atherosclerotic, occlusive or hypoplastic changes and anatomical variations by one radiologists. Angiographic findings revealed vascular variations or ASO in 34 patients, normal in 66 patients and unoptimal enhancement in one patient. Finally, 200 lower extremities were included in this study. Among them CT angiography shows ASO in 14 lower extremities, peroneal artery to posterior tibial artery continuation in 10, peroneal artery to distal anterior tibial artery continuation in 10, early branching of anterior tibial artery in 3, early branching of posterior tibial artery from popliteal artery in 2, communication channel between anterior tibial artery and peroneal artery in 2, two circumflex iliac artery in 2 and early branching of deep circumflex iliac artery in 1. There were other variations such as abscent peroneal artery or dorsalis pedis artery, hypoplastic both anterior tibial artery and dorsalis pedis artery and distal branching of tibioperoneal trunk. In 100 patient, CT angiography confined the operation to the unilateral extremity in 29 patients. And 4 patients were excluded from the candidates. CT angiography is useful methods in preoperative evaluation of the vascular anatomy of the lower leg prior to fibula free flap harvest.