Approximately 15% of individuals aged 18–35 currently report use of methylenedioxymethamphetamine (MDMA). In order to identify and assess the subjective effects of MDMA, the MDMA Beliefs Questionnaire (MDMA-BQ) was developed and validated on a sample of college students. Participants (N = 913) responded to items describing possible outcomes of using MDMA. Principal components analyses (PCA) revealed a five-factor solution. The five scales were named: (a) Global Positive Effects; (b) Safety; (c) Health Risks; (d) Psychological Consequences; and (e) Dose/Mixing Effects. The MDMA-BQ scale scores were associated with level of MDMA use. Overall, nonusers’ scale scores for negative outcomes associated with MDMA were higher than individuals who endorsed having used MDMA once or more, and participants who had used MDMA rated the positive outcome expectancies higher than nonusers. Findings are consistent with previous research and provide evidence of construct validity for the MDMA-BQ. In a second study, scores on the Global Positive Effects, Safety, Health Risks, and Dose/Mixing Effects scales of the MDMA-BQ predicted subsequent self-reported MDMA use and intent to use MDMA in hypothetical scenarios. The MDMA-BQ appears to be a useful psychometric tool in MDMA use research.