This study examines the impact of offenders’ psychological and demographic attributes and their offense history on the effectiveness of Reasoning and Rehabilitation, a cognitive–behavioral intervention. Differential effects were examined for a sample of 940 male parolees randomly assigned to either experimental or comparison conditions. The study used survival analysis to test interactions between treatment and age, race, social class, risk, marital status, prearrest employment status, education, prior violence, interpersonal maturity level, personality, reading level, and IQ. For the entire sample, the difference in recidivism rates (returns to prison up to 33 months) was not statistically significant. The analysis of differential effects, however, uncovered five interaction effects. The treated high-risk, aged 28 to 32 years, assessed as dependent (Jesness Inventory [JI]), and White groups evidenced lower recidivism rates than their comparison group. The treated parolee group assessed with high anxiety (JI) evidenced a higher recidivism rate than their comparison group.