Narcolepsy is a rare sequela of brain injury. We report the case of a 27-yr-old male with post-traumatic narcolepsy who was successfully treated with methylphenidate. This patient sustained moderate brain injury from a motorcycle accident. Subsequently, he manifested the classic tetrad of narcolepsy: cataplexy, excessive daytime sleepiness, sleep paralysis, and hypnogogic hallucinations. There was no premorbid seizure or sleep disorder. There was no family history of sleep disorders. Polysomnography and Multiple Sleep Latency Test confirmed the diagnosis of narcolepsy. Sleep latency (time to sleep onset), rapid eye movement sleep latency (time from sleep onset to rapid eye movement sleep onset), and mean multiple sleep latency were all pathologically shortened (2.5, 66, and 1.2 min, respectively). Twenty-four hour electroencephalographic monitoring and magnetic resonance imaging of the brain were normal, as were serum chemistries. Treatment with caffeine was unsuccessful. He was then started on methylphenidate, 10 mg twice daily, which was increased to 30 mg twice daily over a 4-mo period. Cataplexy and excessive daytime sleepiness started to improve 1 mo after adjustments in methylphenidate dosing. Six months after the initiation of methylphenidate therapy, the patient is completely asymptomatic.