The purpose of the current study is to review the available scientific evidence on the relationship between testosterone and sexual aggression. A systematic search for all primary studies comparing basal testosterone levels in sex offenders and non-sex offenders was undertaken across 20 electronic databases using an explicit search strategy and inclusion/exclusion criteria. A total of seven studies were identified and 11 effect sizes were computed; effects were pooled using both fixed and random effects meta-analysis models. Although individual study findings present a mix of results wherein sex offenders have higher or lower baseline levels of testosterone than non-sex offenders, pooled results indicate no overall difference between groups. Moderators of the analyses suggest possibly lower rates of testosterone in child molesters than controls; however, results are dependent on study weighting. Limitations, policy implications with respect to chemical castration laws, and future directions for research are discussed.