Subcutaneous emphysema and pneumomediastium is a relatively uncommon phenomenon. Most case of pneumomediastium are caused by iatrogenic injury on the cervical region and chest during tracheostomy. It is also well known that emphysema may occur secondary to dental treatment using high-speed air turbine handpiece, but there have been few cases of emphysema extended to involving the mediastinum. These complications are reported to occur mainly in patients after dental procedures, in particular during mandibular third molar extraction. Early recognition and conservative treatment of these problems is essential in preventing life-threatening complications such as airway obstruction, mediastinitis, pneumothorax and cardiac failure. As we report a case of 25-year-old woman with subcutaneous emphysema and pneumomediastium after mandibular third molar extraction using high-speed air turbine handpiece.