Subcutaneous emphysema and pneumomediastinum imply free air within the subcutaneous and the mediastinum. They are well-known associated to trauma and surgery procedure, but relatively rare secondary to dental extraction. A case is described of acute subcutaneous emphysema and pneumomedisatinum after third molar extraction with using a high-speed dental handpiece. We review the literature and discuss the possible mechanism. Although they are rare but serious and easily misdiagnosed in the primary clinics and emergency department, physicians should be more aware of these. (J Intern Med Taiwan 2012; 23: 114-118)