An injury to the spinal accessory nerve is mostly reported after surgical procedures performed in the posterior triangle of the neck. In addition, it may be caused by fractures in the jugular foramina, traumas or skull base tumors. Clinically, paralysis of the trapezius muscle leads to weakness, downward rotation of the scapulae and falling down of the shoulder girdle. A 38-year-old male with left shoulder pain, scapular deviation and weakness in the left upper extremity, whose symptoms developed over a two-year period following a traffic accident, is presented herein. In the electromyography (EMG) study, partial spinal accessory nerve palsy was detected. The patient was treated conservatively for the nerve palsy since the time elapsed rendered surgical intervention inappropriate. We report a case in which spinal accessory nerve palsy developed two years after a traffic accident. Accessory nerve injury following a traffic accident is very uncommon.