This meta-analytic review examined the effectiveness of psychological treatment for sex offenders by summarizing data from 43 studies (combined n = 9,454). Averaged across all studies, the sexual offence recidivism rate was lower for the treatment groups (12.3%) than the comparison groups (16.8%, 38 studies, unweighted average). A similar pattern was found for general recidivism, although the overall rates were predictably higher (treatment 27.9%, comparison 39.2%, 30 studies). Current treatments (cognitive-behavioral, k = 13; systemic, k = 2) were associated with reductions in both sexual recidivism (from 17.4 to 9.9%) and general recidivism (from 51 to 32%). Older forms of treatment (operating prior to 1980) appeared to have little effect. Future directions for improving the quality of sex offender treatment outcome evaluations are discussed.