A 22-year-old woman was involved in a motor vehicle accident and suffered a craniofacial injury. The patient was treated conservatively with a diagnosis of cerebral contusion in the frontal base confirmed with MR images. When the patient regained consciousness one week after the accident, she had a complete form of bitemporal upper quadrantanopia. A bone window level CT scan showed a linear fracture in the middle of the frontal base running longitudinally and extending posteriorly down to the sella turcica and clivus. Axial MR images parallel to the optic pathway revealed a T2 bright lesion in the anterior half of the optic chiasm. The patient recovered gradually and returned to her previous life-style six months later without complaining of diplopia, but her visual field defect was left unchanged. Traumatic chiasmal syndrome is rare and usually presents bitemporal hemianopsia. Very rarely, bitemporal quadrantanopsia has been reported. Given the anatomical structure that the neural fibers from the lower nasal part of the retina run posteriorly in the optic nerve and cross the anterior half of the optic chiasm to enter the contralateral optic tract, the lesion in the optic chiasm seen in the MR images seemed to be the causative lesion of bitemporal upper quadrantanopsia in our patient. The optic chiasm appeared to be injured by a laterally stretching force exerted in an antero-posterior direction when the medial basal fracture occurred.