Patient samples from methadone maintenance and detoxification programs are examined for their patterns of criminal activity before, during, and after treatment. Demographic, sociological, and criminal history variables are tested for their ability to account for changes in arrest patterns over time. While the number of arrestees decline after entering treatment, certain groups remain at high risk of arrest and/or conviction. Patterns of crime as measured by official arrest statistics do not appear stable over time for the treatment cohorts.