A 73 year-old patient with Wolff-Parkinson-White syndrome and paroxysmic supraventricular tachycardia developed an acute reversible encephalopathy within 15 days of initiation of flecainide. The clinical picture was characterized by visual hallucinations, agitation, anxiety, but no disorientation, and a severe cerebello-myoclonic syndrome with total inability to stand up and walk, which was fully reversible on discontinuing the medication.