The link between illicit drug use and impaired employee performance in the workplace has been assumed, but the relation has not been demonstrated clearly in research. This study was an evaluation of the relations between cocaine and opiate use, attendance, and performance in a job skills training program in a population with high rates of drug use.Out-of-treatment injection drug users (N = 42) attended a model therapeutic workplace where they could earn a maximum pay of around $10 per hour, 4 h every weekday, for 30 weeks. At the workplace, participants could complete practice trials on computer-based typing and keypad training programs. Participants were asked to provide urine samples thrice weekly, which were tested for opiates and cocaine.Participants worked for more hours on a program that resulted in a flat hourly wage when their urine was negative for opiates and cocaine than when their urine was opiate and cocaine positive. Attendance was positively associated with opiate-negative samples during the study. When participants attended the workplace, however, their performance was not related to drug use. Participants completed the same number of practice trials, performed at the same accuracy, and typed at the same speed when they were positive and negative for cocaine and opiates.Contrary to common expectations, this study failed to show that the use of opiates or cocaine affected in-training performance, even though opiate and cocaine use predicted reduced attendance under some circumstances.