Aims Ecstasy, the street name for 3,4-meththylenedioxymethamphetamine, has been associated with a range of psychiatric symptoms and impaired psychological health in both problem and recreational users. The purpose of the present paper is to determine how these impairments are related to the history of polydrug use, and the conditions under which individuals ingest ecstasy. Design Associations between the variables of interest were investigated utilizing negative binomial regression. Setting Liverpool and Preston in the NorthWest of England. Participants A convenience sample of 159 recreational ecstasy/polydrug users (80 males, 79 females). The sample was composed primarily of undergraduates. Measurements The dependent variable was the number of reported ecstasy-related adverse effects. Independent variables included quantitative aspects of ecstasy and other drug use, and the various beliefs and behaviours associated with ecstasy use. Findings The number of adverse effects was associated positively with life-time exposure to ecstasy and negatively with period of abstinence from the drug. Adverse effects were more common among those who consumed ecstasy and alcohol concurrently, but were unrelated to other aspects of polydrug use. They were unaffected by whether the user took precautions when using the drug, and onlyweakly related to prior beliefs concerning the effects of ecstasy. Conclusions Greater life-time exposure to ecstasy and consuming the drug concurrently with alcohol increase the likelihood of experiencing adverse effects, including paranoia, poor general health, irritability, confusion and moodiness. Adverse effects decrease with the period of abstinence from the drug.