In a high flow bypass, used for therapeutic occlusion of the internal carotid artery affected by giant or large aneurysms, a radial artery graft provides better long-term patency, but shorter available length compared with a saphenous vein graft. Therefore, a radial artery graft requires a shorter graft route. The purpose of this study was to verify the shortest graft route for a high flow bypass using cadaver dissection. Five cadavers were tested bilaterally, i.e. 10 sides in total. According to the relationships among the mandible, posterior belly of digastric muscle, stylohyoid muscle, and zygomatic arch, we examined 10 types of graft routes. The shortest of the 10 routes was a sub-mandibular route running laterally to both the digastric and stylohyoid muscles, and through the zygomatic arch at the occipital side. The longest route was an over-mandibular route through the zygomatic arch at the frontal side. On average, the former route was 2.5 cm shorter than the latter. Considering graft length limitations, a sub-mandibular route, lateral to both the digastric and stylohyoid muscles, and through the occipital side zygomatic arch, appears to be the most suitable for high flow bypass using a radial artery graft.