The insanity defence: from wild beasts to M'Naghten.

OBJECTIVE: This paper provides an overview of the insanity defence. An historical context is offered and each element of the M'Naghten Rules is discussed, highlighting differing interpretations within various jurisdictions. Discussion is offered on the role of expert evidence in addressing the 'ultimate issue' before the courts. Significant case law in relation to the insanity defence is highlighted.

CONCLUSIONS: Psychiatrists have an important role to play in addressing issues central to the M'Naghten Rules and making these accessible and comprehensible to court and jurors in particular. Insanity is a legal construct designed to determine the extent to which a person may be deemed criminally responsible for a criminal act and is often difficult to reconcile within medical and public paradigms of mental illness and justice. Principles are offered to guide psychiatrists who are called to give evidence in cases where the mental illness defence has been raised.