Traumatic thyroid hematoma is a rare problem in cases of blunt trauma, but it can be a life-threatening condition. We report here on a case of thyroid hematoma that was complicated with unexpected airway obstruction due to blunt trauma on the anterior neck. A 23-year-old man who developed neck painful swelling and dyspnea was admitted to the emergency room with a blunt neck injury after motor-bicycle accident, and he hit his anterior neck against the handle-bar. He had no previous thyroid pathology and other medical problems. On the initial examination, his vital signs were stable and the oxygen saturation was 97.8%. A computed tomography (CT) scan of the neck showed fragmentation and extensive hematoma within the right thyroid gland and dislocation of the trachea. No definite bleeding focus was identified on the angiography that was done through the carotid artery. Two hours later, the patient experienced sudden respiratory distress and the oxygen saturation dropped rapidly. The patient needed emerg encyen-dotracheal intubation and surgical intervention. He successfully underwent right lobectomy of the thyroid gland, and was discharged on the 6th hospital day without any complications. The thyroid function was normal after 3 months. (Korean J Endocrine Surg 2010;10:39-41)