While the idea of violent acts committed by an unwilling assailant in the throes of sleep has been recorded as early as the 1200s, it was not until 1686 that documentation for an English legal case was found. Colonel Cheyney Culpepper, a known and habitual sleepwalker, shot an officer of the guard with a blunderbuss 1 . He was first found insane at the Old Bailey, but then later pardoned by James II. From this point on, there were few legal cases using the sleep state as a defence, with none in the 1700s, no doubt in part due to the scepticism of the public and, indeed, of the scientific community at the time, as to the legitimacy of these conditions 2 .More cases began to spring up in the 1800s, partially attributed to the increase in newspaper circulation both in America and Europe, and the sensationalist stories of sleepwalkers becoming more popular with the general public. While physicians were aware of somnambulism and its potential for violence, and considered it a genuine disorder as early as the 1840s, they were generally informed only by their own experiences and single case reports 3 . Their testimonies were not always enough to sway a jury, with English psychiatrist John Pagan exclaiming "It would be exceedingly difficult to convince a jury of the real existence of such a condition" 4 . At this time, in the view of the public, sleepwalking was considered eccentric rather than malignant, and for the most part harmless. It was not until the 20 th century, when the speciality of sleep medicine was founded, that robust scientific ABStrActSleep medicine is a relatively new field among Medical Sciences. Its legal aspects are still obscure, either for lack of knowledge of the biological mechanisms underlying violent behaviour during sleep or the virtual absence of clear legal and uniformly accepted guidelines as to whether to punish or treat those disorders. An updated review of the pertinent literature was performed to determine the most prevalent pathological conditions involving violence and sleep and to identify their most common precipitating factors, attempting to provide some technical support to aid Brazilian medical-experts or assistants in preparing substantial and scientific-based reports in a legal environment.Keywords: sleep medicine, sleepwalking, behaviour disorder, parasomnia. reSumo A medicina do sono é um campo relativamente novo dentro das Ciências Médicas. Seus aspectos legais encontram-se ainda na obscuridade, seja por falta de conhecimento dos mecanismos biológicos do desenvolvimento dos transtornos de comportamento e da violência praticada em estados alterados de sono, seja por virtual ausência de previsão legal do binômio tratamento/punição. Realizamos revisão atualizada da literatura para determinar as condições patológicas mais prevalentes envolvendo violência e sono, identificar seus fatores precipitantes mais comuns e os critérios médico-legais que podem auxiliar eventuais médicos-peritos ou assistentes na elaboração de pareceres abalizados em âmbito legal.Palavras-chave: medicin...