Post-traumatic pupil dilation is a sign of cerebral hemorrhage. In the early stage, the pupil on the diseased side narrows due to the stimulation of the motoneurotic nerve, but it is not easily detected for a short period of time, and then the motoneurotic nerve is compressed and the pupil on the diseased side expands. The presence of this condition basically identifies cerebral hemorrhage, and the diagnosis can be confirmed with CT and magnetic resonance imaging (MRI) examinations.