This review is aimed at summarizing the current state of knowledge regarding parasomnias, which have been implicated in medicolegal cases as well as providing guidance to those working within common-law jurisdictions regarding the technical aspects of the law. Sleepwalking and sexsomnia as a defence are being raised more frequently in criminal cases and there has been public debate on their validity. Unfortunately, expert evidence on forensic sleep disorders continues to be heavily opinion-based with the potential for miscarriages of justice seen in recent highly publicized cases. There is an apparent inertia in research into violent sleep disorders. We review the current state of forensic sleep science in the United Kingdom (UK) and abroad and discuss the need to formulate guidelines based on available evidence. We also highlight the pressing necessity for more research in this area as well as the need to reform the law, which is the subject of a recent Criminal Law Commission report in the United Kingdom. In time, this will facilitate the efficient, proportionate, and just disposal of violence arising from sleep, thus benefitting both society and the individual sufferer.