This report describes the case of an epileptic patient who, at the age of 16, when he started to use diphenilhydantoin, showed, in the very first days, signs qf intolerance, with sensation of tingling in the extremities. At the age of 36, the patient again made use of this drug and developed symptoms of labyrinthitis, with crises of a rotatory type when inclining his head to the left or when moving it abruptly. The specific treatment for labyrinthitis recomended by an otorhinoraryngologist proved to be ineffective and the clinical picture aggravated progressively. Six months later, the patient's psychic examination revealed a slight torpor, slowness of reasoning, inability to work and a reactive depression. There has also been observed, from the neurological point of view, a slight deviation of the gait towards the left, and a slight enlargement in the base of sustentation. Besides this, vertiginous crises and vomits were so frequent that in the last two months he has had to be hospitalized several times to be hydrated. The interruption of diphenilhydantoin and the continuation of phenobarbital as the exclusive medication (he was already making use of it), determined the rapid regression of the symptoms mentioned. Such facts permitted us to conclude that the labyrinthitis was provoked by the use of diphenilhydantoin and must be included in the extensive list of side effects provoked by this drug.