Follow-up interview data for 1,155 opioid addicts showed that about three-fourths of the sample reported some criminal behavior during a 4-year period after leaving drug abuse treatment. Males had a higher prevalence of“major”crimes (including crimes against persons, robbery, mugging, burglary, theft, or dealing drugs) than did females, while females reported a higher percentage engaged in the so-called“victimless”crimes (primarily based on prostitution or pimping). Criminal behavior was primarily profit-related and strongly associated with drug use, especially opioid drugs. Drug users reported more criminal behavior than nonusers, and criminality and drug use increased and decreased together among persons who showed changes in drug use during the follow-up period.