Atlanto-axial posterolateral dislocations associated with an odontoid fracture are rare traumatic lesions of the upper cervical spine. Their therapeutic management is discussed.We report the case of a 28-year-old man with no significant medical history admitted to the emergency room with upper cervical spinal trauma following a frontal collision of two vehicles. We found a left arm monoparesis and a posterolateral atlanto-axial dislocation associated with a fracture of the displaced type II odontoid. The patient was treated by a retropharyngeal approach anteriorly after reduction by intraoperative traction by Gardner wells tongs maintained by a weight of 10 kg. The evolution was marked by a complete recovery of the left arm monoparesis at two months followed by physiotherapy. Keywords: Left arm monoparesis, Posterolateral atlanto-axial dislocation, Intraoperative traction, Retropharyngeal anterior approach