At the turn of the 21st century, the United States experienced a rapid increase in the use of the illicit stimulant known most commonly as ecstasy or MDMA (3-4 methylenedioxymethamphetamine). There are some research indications concerning criminal behavior among ecstasy users. This study explored this dimension using data from 7,794 arrested men, age 16 to 25, in the 2001 Arrestee Drug Abuse Monitoring (ADAM) sample and 9,764 male respondents of similar age in the 2001 National Household Survey on Drug Abuse (NHSDA). Ecstasy use was found to be positively related to drug market participation and arrest for drug-related crimes, but negatively related to arrest for violent and property crimes. The findings suggest that the most direct pathway between ecstasy use and crime lies in nonviolent but economically aggressive participation in drug markets. Researchers, policymakers, and practitioners need to better understand the linkages between ecstasy use and crime in order to more effectively address ecstasy’s impact on the social costs of crime. Tables, glossary and references