This paper reports a case of a true aneurysm of the intracranial internal carotid artery that occurred after a closed head injury. The probable etiology of this unusual lesion is discussed in respect to other partial and complete vessel wall injuries. The diagnosis of a traumatic aneurysm must be suspected when a delayed intracranial hemorrhage occurs after a head injury. The treatment of most intracranial aneurysms should be early, direct operation. Traumatic aneurysms of the internal carotid artery, however, are uniquely treacherous, and they may warrant an indirect approach when discovered soon after injury.