“The misery of the insane more thoroughly excites our pity than any other suffering to which humanity is subject* but it is necessary that the madness should be acknowledged to be madness before the pity can be felt”1. Basically, two principles may be said to underlie the general exceptions to criminal responsibility. Firstly, the circumstances surrounding the commission of the act may amount to a legal justification for its commission. Secondly, the circumstances may be incompatible with the existence of mens rea. The plea of insanity falls within the latter category. The plea expresses the principle that one who has lost his “reason” should not be criminally condemned. The insanity plea is a focal point on which many different policy questions converge. Some of these questions are: (a) what is the most efficient way of protecting society from those whose state of mind leads them to do social harm? 1. Trollope. “He knew he was Right” Cited by Williams, G. (1978) Textbook of Criminal Law stevenS, London. F. 587. ‘ iv – (b) what is the role of medical expert in the inquiry into insanity? (c) should the prosecution have the right tc introduce the plea, even against the wishes of the accused? (d) in the disposal of the insanity cases, how best can the individual’s right be reconciled with the need to rehabilitate him and the protection of the Community? These are complex problems and are all interwined. The plea of insanity and the controversies generated by it justify their significance, in part, on the fact that in those cases in which the plea is invoked, fundamental principles of justice and morality are at stake. The availability of the plea expresses albeit, symbolically, the concern of the law with citizens as rational creatures. The plea of insanity, like other general defences to criminal responsibility, is open to an ad person in all criminal proceedings although it is often pleaded only to the more serious offences carrying the death Penalty. In other words, the more serious the charge, the greater is the necessity to examine the accused’,”. :.ental state. This need is rather imperative in Homicide cases. The insanity plea is raised either alone or with similar defence ;. – V The expression “insanity is capable of covering both insanity at the time of trial and insanity at the time of the offence. It is with the latter sense that the greater part of the literature on the subject is predicated. This distinction must be kept in focus for a thorough appreciation of the subject. Organisational Structure. The dissertation is divided into seven chapters. Chapter I which is the introductory chapter, traces generally the origin of the Penal as well as the Criminal Codes, the relationship between the two Codes, and the relationship between the Nigerian Codes and other Legal Systems. Chapter II deals generally with the problem of definition of insanity and the rationale for the plea of insanity. It also traces the genesis Of the concept, its various metamorphosis, culminating in the M’Naghten ilejs. The Chapti ith an i ;ion of the main limitations of the English rules. Chapter III discusses the insanity defence in Nigerian Law vizs the exposition of the Salient features of the nal Code and Criminal Code Provisions on ‘the insanity defence. – vi – Chapter IV examines the defence of insanity as found in other jurisdictions. Particular attention is paid to the concept of insanity under customary and islamic law and. insanity in some Common Law jurisdictions such as Ghana, Sudan and America. Chapter V treats the evidence and procedure of proving insanity viz: the trial of the issue of insanity, the burden and quantum of proof and the methods of proving insanity. Chapter VI examines some issues related to insanity defence. Examples of such are automatism, intoxication (delirium Tremens) and infanticide (the effect of lactation). Chapter VIII the concluding Chapter, is a summary of the dissertation and the conclusions drawn there from. It also includes the researcher’s recommendations for reform. All these are humbly made with a view to curing some of the patent defects now existing in the Law.