Clinical case reports suggest that regular MDMA use can be associated with chronic psychiatric symptoms which persist after the cessation of drug use. Neuropsychological comparisons of regular MDMA users and controls also suggest that MDMA use may lead to memory deficits, with other cognitive processes relatively unaffected. This paper reviews these studies and discusses a number of methodological issues that impact on the interpretation of the findings. Methods for examining the biological effects of MDMA use in man are also outlined. Future research should clarify whether MDMA use has long term psychological effects, and if these are related to changes in central serotonergic function.