The aims of this study were to investigate the vascular communication between the superficial temporal artery (STA) and the posterior auricular artery (PAA) and to determine the vascular territory of various retroauricular flaps for flap design. A series of eight adult fresh cadavers were perfused with a mixture of lead oxide, gelatin, and water through the common carotid and femoral arteries. The full thickness of scalp and facial skin was removed with the STA and the PAA. A radiograph was taken of each specimen. After the retroauricular flap with the PAA from the posterior auricular and mastoid regions was elevated, another radiograph was taken of the specimen. Our radiographic assessment revealed two patterns of vascular anastomosis between the STA and PAA. The auricular anastomoses were found at the upper portion of the posterior surface of the ear, where some reticular anastomoses occurred between auricular branches derived from the STA and the PAA. The scalp anastomoses were located in the scalp superior to the ear, where some reduced caliber choke anastomoses or true anastomoses existed between the parietal branch and the terminal branches of the PAA. The results of this study will be helpful for better understanding of the vascular communication between the STA and the PAA and the vascular territory of retroauricular flaps. Our findings will also provide anatomic information and guidance for the design of reliable flaps.