The study compared recidivism rates after 2 years for two groups of adult male offenders who were serving a custodial sentence of 2 years or more. The treatment group (n=667) consisted of offenders who had voluntarily participated in 1 of 2 treatment programs that targeted cognitive deficits related to offending behavior. The comparison group (n=1,801) was composed of offenders who had not participated in the treatment programs but were matched to the treatment group on a number of empirically relevant variables. The study found that the treatment programs produced a significant reduction in the probability of recidivism when other relevant variables were controlled. For treated offenders, the percentage point reduction in recidivism was 14 percent for medium-low-risk offenders and 11 percent for medium-high-risk offenders. The study shows the efficacy of cognitive skills programs operated in prisons in England and Wales since their inception and including the first year of the accredited program process. It is anticipated that future outcome studies of subsequent cognitive skills program participants may replicate or improve upon these results due to the accreditation process being better established. Additional research could explore in greater detail the factors associated with a positive treatment outcome, including which types of offenders benefit most from this type of treatment. 5 tables, 1 figure, 24 references, and appended independent variables used in the logistic regression model to predict reconviction within 2 years