If all sexual offenders are dangerous, why bother assessing their risk to reoffend? Follow-up studies, however, typically find sexual recidivism rates of 10%-15% after five years, 20% after 10 years, and 30%-40% after 20 years. The observed rates underestimate the actual rates because not all offences are detected; however, the available research does not support the popular notion that sexual offenders inevitably reoffend. Some sexual offenders are more dangerous than others. Much is known about the static, historical factors associated with increased recidivism risk (e.g., prior offences, age, and relationship to victims). Less is known about the offender characteristics that need to change in order to reduce that risk. There has been considerable research in recent years demonstrating that structured risk assessments are more accurate than unstructured clinical assessments. Nevertheless, the limitations of actuarial risk assessments are sufficient that experts have yet to reach consensus on the best methods for combining risk factors into an overall evaluation.