This study assesses the frequency that users of illicit drugs display unprofessional behaviors in an employment setting. This research was conducted in the therapeutic workplace, a model employment-based treatment program for chronically unemployed adults with long histories of illicit drug use in 2003. Fifty-three unemployed adults in methadone treatment, who were opiate and cocaine dependent, showed signs of injection drug use, and recently used cocaine were hired to work for 4 hours every weekday for 7 months. Results show that while the overall incidence of many undesirable behaviors is low, a small percentage of participants had serious workplace behavior problems that might limit their success in community workplaces. This study suggests that unprofessional behavior in the workplace could contribute to chronic unemployment in this population. The study's limitations are noted and future needed research is suggested.