Three patients had longstanding (37 to 50 years), highly disabling narcolepsy, poorly controlled by treatment. The clinical histories were typical, consisting of sleepiness, cataplexy, sleep paralysis, hypnagogic hallucinations, disturbed nocturnal sleep, and HLA-DR2 tissue typing. Polygraphic findings confirmed the diagnosis. Neurologic examination, spinal fluid, and evoked potentials were normal. On MRI scanning, all three patients showed overlapping bilateral and symmetric brainstem T2 hyperintensities circumscribed to the ventrolateral aspect of the midrostral pons. The nature of the lesions remains uncertain but their location corresponded to the pontine oral reticular formation, where the neuronal network generating REM sleep is located. This is the first report of MR signal abnormalities in patients with idiopathic narcolepsy and suggests a causal relationship between the disease and the central pontine lesions.