The goal of meta-analysis is to standardize and interpret the findings of diverse studies in an objective, verifiable manner so that replication of the review is possible. Meta-analysis aims to achieve these goals by expressing the outcome of the individual studies under review by common measures of effect size. The review of the meta-analysis literature on treatment effectiveness includes those studies that used a measure of effect size and referred to their technique as meta-analysis. A measure of recidivism was used. The meta-analyses reviewed constitute a subset of the offender-treatment literature. The data examined indicate that recidivism is most likely to be reduced through correctional treatment. The findings suggest that offenders should be assessed as to risk level and need and that the intervention should be behavioral in nature with an emphasis on cognitive and skill development. Institutional treatment programs should be continued, and program planners and evaluators should cooperate in all operational phases of the treatment process. 32 references.