Studies conducted in humans or in animals explored the presence, nature and potential causes of 3,4-methylenedioxymethamphetamine (MDMA) toxicity. According to literature, there are four principal types of such serious toxicity: hepatic, cardiovascular, cerebral and hyperpyrexic. The molecular mechanisms involved in the genesis of these toxic effects are not yet fully clarified, but the oxidative stress, excitotoxicity, and mitochondrial dysfunction appear to be causal events that converge to mediate MDMA-induced toxicity. Studies conducted on animals demonstrated that the acute administration of MDMA elicits cardiovascular responses that are similar to those elicited by d-amphetamine, and that these responses appear to involve catecholaminergic and non-catecholaminergic-dependent mechanisms. Although there is undeniable evidence of MDMA-induced cardiac toxicity, the mechanism responsible remains to be clarified. While many reports both in humans and in animals have demonstrated MDMA-induced liver damage, the underlying mechanism accounting for hepatic toxicity is poorly understood. Various mechanisms may contribute to MDMA-induced liver toxicity, including the metabolism of MDMA, the increased efflux of neurotransmitters, the oxidation of biogenic amines, and hyperthermia. The molecular mechanisms involved in the genesis of these toxic effects are not yet fully clarified, but the oxidative stress, excitotoxicity, and mitochondrial dysfunction appear to be causal events that converge to mediate MDMA-induced neurotoxicity, as measured by loss of various markers of dopaminergic and serotonergic terminals. The evidence is overwhelming that MDMA produces acute and long-lasting toxic anatomic effects in animals and humans. Anatomical and functional MDMA consequences must be better understood.