According to perceived-deterrence theory, the likelihood that an offender will engage in drug use or illegal activity is influenced by the perceived certainty of being detected for infractions or recognized for accomplishments, the perceived certainty of receiving sanctions for infractions or rewards for accomplishments, and the anticipated magnitude of the sanctions and rewards. This study evaluated drug court participants' perceived deterrence at monthly intervals during their enrollment in drug court. Exploratory cluster analysis (N = 255) on the longitudinal scores yielded five subtypes of drug offenders characterized either by consistently elevated perceived-deterrence scores, consistently moderate scores, consistently low scores, increasing scores, or decreasing scores. The best outcomes were associated with consistently elevated scores, whereas the worst outcomes were associated with scores that declined over time as the participants became accustomed to the program. The clusters also differed in predicted directions on demographic variables. The correlational design does not permit inferences of causality; however, the results lend credence to perceived deterrence as a potential explanatory mechanism for the effects of drug courts. Copyright © 2005 John Wiley & Sons, Ltd.