The purpose of this article is to review legislation on 'dangerous sex offenders' critically. Most modern legislation determines an individual to be 'dangerous' if he or she is at unacceptably high risk of committing further sexual violence. While the decision is judicial in practice, clinical testimony is utilised to inform courts' decision-making. Dangerousness may be a normative (legal) construct, but it is reliant on clinical assessment. Offenders are not at risk only due to historical factors; the possibility of committing sexual violence in the future is likely affected by temporal factors such as response to therapy, substance misuse, and proximity to victims. It is not clear that mental illness would place an offender at risk, although certain personality disorders are considered to be risk factors. In reporting actual risk, clinicians need to consider a range of variables, and not exclusively use actuarial measures or unstructured clinical interviews.