"Ecstasy" (MDMA) and related drugs are amphetamine derivatives that also have some of the pharmacological properties of mescaline. They have become popular with participants in "raves," because they enhance energy, endurance, sociability and sexual arousal. This vogue among teenagers and young adults, together with the widespread belief that "ecstasy" is a safe drug, has led to a thriving illicit traffic in it. But these drugs also have serious toxic effects, both acute and chronic, that resemble those previously seen with other amphetamines and are caused by an excess of the same sympathomimetic actions for which the drugs are valued by the users. Neurotoxicity to the serotonergic system in the brain can also cause permanent physical and psychiatric problems. A detailed review of the literature has revealed over 87 "ecstasy"-related fatalities, caused by hyperpyrexia, rhabdomyolysis, intravascular coagulopathy, hepatic necrosis, cardiac arrhythmias, cerebrovascular accidents, and drug-related accidents or suicide. The toxic or even fatal dose range overlaps the range of recreational dosage. The available evidence does not yet permit an accurate assessment of the size of the problem presented by the use of these drugs.