The predominant severe acute adverse effect following ingestion of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) by recreational users is hyperthermia which can induce other associated clinical problems and occasionally death. There is no pharmacologically specific treatment. MDMA also induces dose-dependent hyperthermia in experimental animals. This review examines the consequences of MDMA administration on body temperature in humans and rodents. In rats hyperthermia results primarily from dopamine release and is influenced by dose, ambient temperature and other housing conditions. The response is increased in rats with a prior MDMA-induced neurotoxic lesion of 5-hydroxytryptamine (5-HT) nerve endings. Increased MDMA-induced locomotor activity appears to play no role in the hyperthermic response. However, the size of the acute hyperthermic response plays a major role in determining the severity of the subsequent neurotoxicity. These results suggest that any MDMA-induced hyperthermic response will be enhanced in hot, crowded dance club conditions and that ingesting the drug in such conditions increases the possibility of subsequent cerebral neurotoxic effect.