Risk assessment and treatment for sexual offenders should focus on individual characteristics associated with recidivism risk. Although it is possible to conduct risk assessments based purely on empirical correlates, the most useful evaluations also explain the source of the risk. In this review, the authors propose that the basic requirements for a psychologically meaningful risk factor are (a) a plausible rationale that the factor is a cause of sexual offending and (b) strong evidence that it predicts sexual recidivism. Based on the second of these criteria, the authors categorize potential risk factors according to the strength of the evidence for their relationship with offending. The most strongly supported variables should be emphasized in both assessment and treatment of sexual offenders. Further research is required, however, to establish causal connections between these variables and recidivism and to examine the extent to which changes in these factors leads to reductions in recidivism potential.