Massive subdural hematomas are known to cause hemorrhagic shock in infants and young children. Traumatic cerebral aneurysms are rare and are often noticed in the subacute phase with disorientation due to the rupture of a pseudoaneurysm. No previous studies appear to have clarified the diagnosis of and therapeutic interventions for traumatic cerebral aneurysms identified from computed tomography (CT) on admission. The present case involved an open skull fracture resulting in hemorrhagic shock due to subcutaneous extravasation from an anterior cerebral artery (ACA) pseudoaneurysm.A seven-year-old boy was accidentally struck by a car after running out into a road. He had an open fracture of the skull and contrast-enhanced CT of the head showed subcutaneous extravasation from the ACA. The patient developed hemorrhagic shock that resolved following the embolization of the ACA with n-butyl-2-cyanoacrylate. Head trauma can cause hemorrhagic shock in the presence of an open wound due to a skull fracture. Contrast-enhanced CT of the head on admission is useful for diagnosis.