Gilles de la Tourette's syndrome (GTS) was diagnosed in a 12 year-old male who complained of peculiar involuntary vocalization. Aerodynamic and sonographic examinations of involuntary speech were performed to clarify the mechanism of the disease. The results showed that words were produced with expiratory air flow. Otolaryngologists must know the symptoms of this disease, because GTS patients often consult otolaryngologists first because of involuntary vocalization.