Pneumomediastinum with subcutaneous emphysema is a rarely observed complication of dental treatment. It is a potentially dangerous condition, but the majority of cases are self-limiting and benign. We present a case of pneumomediastinum and cervicofacial emphysema that occurred after dental treatment. The rapid onset of swelling and dyspnoea are often misinterpreted as an allergic reaction to the anaesthesia used during the procedure. Physicians and dentists should be aware that cervicofacial emphysema can cause swelling after dental procedures and may mimic an allergic reaction.