3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) is a known neurotoxin in animals. This review discusses the history, pattern of use, pharmacology, acute and long-term effects of MDMA. Emphasis is given to the concern that MDMA may induce long-term cognitive and psychiatric effects. MDMA is an illegal substance, and investigations of the effects of exposure in human beings have limitations and weaknesses. There are numerous studies suggesting a correlation between MDMA exposure and psychopathology, and that the psychotropic effects may be long-lasting or permanent. However, it is not possible to conclude that there is a causal relationship between exposure and the increased psychopathology observed in MDMA users. Longitudinal studies are needed to assess whether MDMA causes persistent cognitive impairment and/or psychiatric symptoms in human beings.