A rare case of a 14-year-old boy with a spontaneous (true) aneurysm of the superficial temporal artery is presented. The mass in the right parietal region was pulsatile and gradually enlarged in size for the last several months without any notable history of head trauma. The mass was successfully removed by surgery and has proved histopathologically to be a true aneurysm. While almost all cases of the superficial temporal artery aneurysm reported are traumatic ones, the true aneurysm of this artery which is verified by angiography is extremely rare. The pathology, etiology and treatment of this true aneurysm of the superficial temporal artery were discussed.