3,4-methylenedioxyamphetamine (MDMA) or "ecstasy" damages serotonin neurons in all animal species and there is growing evidence that this finding also applies to humans. This fact, together with the increasing extended use in the young population, has important repercussions in the appearance of specific psychopathologic and cognitive disturbances associated to its use. The authors present two clinical cases, in which psychopathological and cognitive symptoms are detected in MDMA users that support this hypothesis. Problems in the diagnosis of psychiatric disorders associated to MDMA and its clinical and therapeutic implications are discussed.