We report a case of traumatic aneurysm in a 50-day old male infant arising from the peripheral portion of right middle cerebral artery. The infant had suffered a major head injury with an iron bar before coming to the hospital. On admission he presented with generalized tonic-clonic seizure 15 days after the head trauma. Computed tomography(CT) scan demonstrated a round, mixed-density hematoma in the right temporoparietal cortex. During operation, an aneurysm was found within the hematoma under the operating microscope, and the aneurysm was assumed to be of traumatic origin. The aneurysm arising from the peripheral right middle cerebral artery was ligated and cauterized, and the hematoma was evacuated. After the operation, the infant had no incidence of any seizure attack nor any focal neurologic deficit. The incidence pathogenesis, clinical diagnosis, and treatment of traumatic aneurysm is discussed together with a review of the literature.