The defence of insanity is one of the most technical and controversial issue in legal jurisprudence and practice from time immemorial. How does a prosecutor, defence counsel and even the judge who is only versed in law disproof, proof and decides the case of an accused person who hides under the protection of the plea of insanity. Another problem arises when the psychologist consultant gives his expert evidence as to the state of the accused person’s reasoning particularly at the point of committing a crime and after the commission of the offence. In this study, it is therefore pertinent to explore the provisions of the law in relation to the plea of this insanity in a 21st century Criminal Justice Administration in Nigeria so as to ensure that justice is not only done to the accused person but manifestly be seen to be done to the victim or his family. It is recommended that there should be an amendment of the provisions of Section 28 and section 51 of the Criminal and Penal codes respectively to include other types of insanity that have been asserted by medical experts as capable of impairing a man’s capacity to understand the nature of his acts. The work concludes that the plea of insanity should not be abolished but reformed to conform to the current trends of modern societies.