Cases of cervicofacial subcutaneous emphysema occurring during dental treatment often result from the use of air-water cooled dental drills during tooth extraction. A case is presented in which a compressed air syringe, used to dry the field, caused diffuse cervicofacial emphysema with retropharyngeal and mediastinal extension. The point of entry appeared to be a 4 mm superficial laceration of the buccal mucosa. Despite the size of the wound, a significant amount of air was able to enter the tissues and spread quite distantly. Though many cases of subcutaneous emphysema go unnoticed, diffuse extension, especially with involvement of deep neck structures and with thoracic extension, must be recognized as they can be potentially life-threatening.