Twelve heavy recreational ecstasy drug users (30-1000 occasions), 16 light ecstasy users (1-20 occasions) and 22 non ecstasy user controls, with group mean ages around 21 years, were compared. Three self-rating questionnaires were completed when drug-free: the SCL-90 (an outpatient psychiatric symptom checklist), the impulsiveness venturesomeness and empathy (IVE) scale; and the uplifts, hassles, stresses and cognitive failures questionnaire. Heavy Ecstasy users reported significantly higher scores than controls on the following SCL-90 factors: paranoid ideation, psychoticism, somatisation, obsessionality, anxiety, hostility, phobic anxiety, altered appetite and restless sleep, together with greater IVE impulsiveness. Light ecstasy users generally produced intermediate scores, with significantly higher scores than controls on two factors and significantly lower scores than heavy ecstasy users on another two. Previous reports have described various psychiatric and psychobiological disorders in recreational ecstasy users, but it is not known how typical they are, being mainly based on individual case studies. This is the first study to describe psychological problems in a non clinical sample of young recreational ecstasy users. However, our ecstasy users were polydrug users, with both groups showing significantly greater usage of amphetamine, LSD and cocaine, than the controls. These other illicit drugs probably contributed to their adverse psychobiological profiles, while there is also the possibility of pre-existing differences between ecstasy users and non users. However, since repeated MDMA can cause serotonergic neurotoxicity in laboratory animals and man, these problems may reflect reduced serotonin activity induced by regular ecstasy use.