ABSTRACT Reactive criminal thinking (RCT) represents the impulsive, irrational, and emotional aspects of antisocial cognition. The current study tested major mental illness and its interaction with prior substance abuse as possible predictors of future recidivism, with RCT serving as a mediator and substance abuse as a moderator. Using Cox proportional hazards regression, it was determined that RCT mediated the relationship between major mental illness and recidivism in a group of 1,435 male federal prison inmates. Substance abuse × mental illness interaction did not predict RCT or recidivism at the traditional .05 level of significance. Findings from this study indicate that major mental illness promotes recidivism by stimulating increased levels of RCT which then goes on to predict recidivism.