Crimes carried out during or arising from sleep highlight many difficulties with our current law and forensic sleep medicine clinical practice. There is a need for clarity in the law and agreement between experts on a standardised form of assessment and diagnosis in these challenging cases. We suggest that the time has come for a standardised, internationally recognised diagnostic protocol to be set as a minimum standard in all cases of suspected sleep-related forensic cases. The protocol of a full medical history, sleep history, psychiatric history, neuropsychiatric and psychometric examination and electroencephalography (EEG), should be routine. It should now be mandatory to carry out routine polysomnography (PSG) to establish the presence of precipitating and modulating factors. Sleepwalking is classified as insane automatism in England and Wales and sudden arousal from sleep in a non-sleepwalker as sane automatism. The recent case in England of R v. Lowe (2005) highlights these anomalies. Moreover, the word insanity stigmatises sleepwalkers and should be dropped. The simplest solution to these problems would be for the law to be changed so that there is only one category of defence for all sleep-related offences--not guilty by reason of sleep disorder. This was rejected by the House of Lords for cases of automatism due to epilepsy, and is likely to be rejected for sleepwalkers. Removing the categories of automatism (sane or insane) would be the best solution. Risk assessment is already standard practice in the UK and follow up, subsequent to disposal, by approved specialists should become part of the sentencing process. This will provide support for the defendant and protection of the public.