The recreational use of MDMA/Ecstasy (3,4-methylenedioxymethamphetamine) is associated with many psychobiological problems, but there is a paucity of data on how these relate to the level of past use. Objectives: to assess the incidence of Ecstasy-attributed problems as reported by novice, moderate and heavy users. Methods: 763 unpaid volunteers took part in a WWW study of recreational drug use. This report is based on the 282 Ecstasy users from that sample, who comprised 109 novice users (1-9 occasions), 136 moderate users (10-99 occasions), and 36 heavy users (+100 occasions). Yes/no responses were automatically recorded to a series of questions covering psychobiological problems experienced when drug-free, which were attributed by the respondents to their Ecstasy use. Results: Depression, memory problems, anxiety, mood fluctuation, poor concentration, infections, tremors/twitches and weight loss, were all significantly associated with the extent of Ecstasy use. Thus memory problems attributed to Ecstasy were reported by 19% of novice users, 52% of heavy users and 73% of heavy users (chi-square 42.74, df = 2, p < 0.001); many of the other variables showed similar trends. Conclusions. The incidence of problems attributed to Ecstasy use, is directly related to the number of occasions it has been used.