Night guards are commonly prescribed as a palliative measure for bruxism, temporomandibular joint symptoms, and associated disorders. We describe a patient with a 10- to 12-year history of night guard use with concurrent unilateral side-locked migrainous headaches with autonomic symptoms characteristic of trigeminal autonomic cephalgia. These headaches were refractory to numerous pharmacological interventions. Upon self-initiated cessation of night guard use, there was complete remission of headaches. We believe the headaches were initiated by night guard-initiated irritation of the trigeminal nerve and a trigeminal autonomic reflex resulting in unilateral migrainous headache with autonomic signs.