To be included in the review, a study had to identify a group of male sex offenders, include a follow-up period, and report sufficient statistical information, such as sample size and recidivism rate. Study results were then summarized by using standard statistical procedures. To increase the reliability of the findings, only variables examined in at least 10 research studies are presented in this article. Findings show that the sex offenders most likely to recidivate sexually are those with a history of sex and non-sex offenses, who are young, and who victimized adult women or extrafamilial boys. The offenders most likely to recidivate generally are also young sex offenders with a history of sex and non-sex offenses. Although each factor identified in this study was reliably related to recidivism, none of the effects were strong enough to justify using any single predictor on its own. Sex offender risk assessment is most accurate when it considers a range of relevant factors. The design of this review did not allow for the calculation of the predictive power of a combination of the best individual predictors; however, other research suggests that when the best predictor variables are combined, it is possible to identify both a high-risk group (with a probability of sexual or violent reoffending greater than 80 percent) and a low-risk group (with a long-term recidivism rate of less than 20 percent). All the factors associated with sexual recidivism were stable, historical variables. Such static risk factors are useful and easy to assess, but they provide little information about when recidivism will occur or how it can be reduced. To answer such questions, more information is needed about dynamic (changeable) risk factors. 3 tables and 7 footnotes