As part of an ongoing National Institute on Drug Abuse study on the reliability of DSM substance use disorders, 173 adolescents and young adults have been interviewed to date with the CIDI-Substance Abuse Module (SAM) to determine use and abuse of and dependence on 'club drugs' and other substances. Respondents are recruited from a substance abuse program, high school ads, college dorm flyers, the internet and chain referral. Retest interviews after 5 days determined the reliability of responses. Ecstasy use was reported by 52 respondents (30%); of these users 52% were female and 23% were non-white. Nearly all users (94%) reported recent Ecstasy use. Among Ecstasy users, 'continuing to use despite knowledge of physical or psychological harm' was the most prevalent dependence criterion (63%), with excellent retest agreement (kappa = 0.66). Withdrawal (59%) and tolerance (35%) were also commonly reported dependence criteria. Hazardous use was the most commonly reported abuse symptom. Most surprising were the rates of Ecstasy use disorders: 43% met DSM-IV criteria for dependence; 34% met criteria for abuse; only 23% met neither. This is the first effort to assess the reliability of Ecstasy abuse and dependence, and the first to determine abuse and dependence using criteria specific to Ecstasy. The importance of additional studies and the relevance of such work to DSM-V are discussed. Copyright 2001 John Wiley & Sons, Ltd.