The parasomnias most frequently associated with forensic consequences are the disorders of arousal (confusional arousals, sleepwalking/sleep terrors) and their variant sexsomnia, parasomnia due to drug or substance and REM sleep behavior disorder (RBD). There are numerous historical cases documenting sleep-related crimes dating back to the seventeenth century. The insanity defense and automatism remain relevant to criminal liability today, but the Model Penal Code (MPC) definitions still rely on ideas that have not kept up to date with developments in neuroscience. It is important that experts providing evidence for apparent sleep-related forensic cases be acutely aware of and follow guidelines laid down by their respective professional and regulatory bodies in their particular jurisdictions. The assessment of a person accused of a violent act that may have arisen from sleep requires a systematic and thorough evaluation of all possible diagnoses.