After the short-term administration of 20mg/d prednisolone (orally) in a previously non-steroid-treated patient with iron storage disease, the steroid, which is omnipresent in clinical practice, led to paradoxical foudroyant symptoms, but above all to a reduction of 80% in the extreme narcoleptic symptomatology, not however in the cataplectic component. Masked primary adrenal insufficiency was revealed. An improvement in narcoleptic symptoms of about 50% was also maintained under oral hydrocortisone-only substitution therapy.