The law on automatism is undergoing change. For some time there has been a conflict between the medical and the legal views. The medical profession believes that the present division between sane and insane automatism makes little medical sense. Insane automatism is due to an internal factor, that is, a disease of the brain, while sane automatism is due to an external factor, such as a blow on the head or an injection of a drug. This leads to the situation where, for example, the hypoglycaemia resulting from injected insulin would be sane automatism, while hypoglycaemia while results from an islet tumour would be insane automatism. This would not matter if the consequences were the same. However, sane automatism leads to an acquittal, whereas insane automatism leads to committal to a secure mental hospital. This article traces the development of the concept of automatism in the 1950s to the present time, and looks at the anomalies in the law as it now stands. It considers the medical conditions of, and the law relating to, epilepsy, alcohol and drug automatism, hypoglycaemic automatisms, transient global amnesia, and hysterical automatisms. Sleep automatisms, and offences committed during a somnambulistic automatism, are also discussed in detail. The article also examines the need of the Courts to be provided with expert evidence and the role that the qualified medical practitioner should take. It clarifies the various points which medical practitioners should consider when assessing whether a defence of automatism is justified on medical grounds, and in seeking to establish such a defence. The present law is unsatisfactory, as it does not allow any discretion in sentencing on the part of the judge once a verdict of not guilty by virtue of insane automatism has been passed. The judge must sentence the defendant to detention in a secure mental hospital. This would certainly be satisfactory where violent crimes have been committed. However, it is inappropriate in many cases where non-violent confusional crimes, such as petty larceny, have been committed. Suggestions are made for desirable changes in the law.