To examine the effects of botulinum toxin injection application for the treatment of upper airway obstruction due to hyperactive lateral pterygoid muscle contraction, we applied botulinum toxin injection. A 20 year-old male patient had involuntary mouth opening after a diabetic coma. His mouth opened excessively (84 mm) particularly when he was in a nervous or stressed condition. This resulted in a bilateral temporomandibular dislocation and, consequently, upper airway collapse. The differential diagnosis of jaw-opening oromandibular dystonia was made. Botulinum toxin type A was bilaterally injected into the lateral pterygoid muscle. The excessive mouth opening was reduced, and the patient showed no temporomandibular joint (TMJ) dislocation or experienced any further airway collapse after the injections. We successfully applied botulinum toxin to a patient with upper airway obstruction and TMJ dislocation relative to jaw-opening dystonia.