Whiplash injury is produced by the hyperextension of the neck followed by flexion. These patients have no abnormality in radiologic evaluation. We collected 39 patients and divided into two groups; Group 1 (neck pain without radiculopathy) and Group 2 (neck pain with radiculopathy). Thermal differences at neck and arm were checked with IR thermography. 1 patient was taken the IR thermography periodically until recovery from his symptom. Group 1 showed that subjective painful area on the neck was changed to hyperthermic, but the arm temperature was normal. Group 2 showed that subjective painful area on the neck was changed to hyperthermic, and painful arm was changed hyperthermic, which can be differentiated from hypothermic change in cervical disc herniation patients. Thermal differences were gradually reduced with the same consequence of the patient’s symptom recovery. IR thermography can be used to diagnose the whiplash injury and also to determine a symptom recovery. It is possible to differentiate the whiplash injury with radiculopathy and pre-existing cervical disc disease.