Following decades of protracted debate, the introduction of the Criminal Law (Insanity) Act 2006 (the ‘2006 Act’) has once again placed the turbulent relationship between psychiatry and the law under the legal microscope. The long anticipated arrival of the 2006 Act brought with it into Irish law new definitions of insanity 1 and fitness to be tried2 in addition to a new plea of diminished responsibility.3 The question of whether the accused was suffering from a ‘mental disorder’ at the time he executed the act (or at the time of trial in the case of fitness to be tried) is the primary focus of these sections of the 2006 Act. Defined as including mental illness, mental disability, dementia or any disease of the mind (apart from intoxication),4 ‘mental disorder’ presents itself as a medical or psychiatric term within a legislative setting. The prominent positioning of ‘mental disorder’, together with the retention of the term ‘insanity’, demonstrates that the basis of any discussion of the 2006 Act must feature an examination of the hegemonic relationship between the two powerhouses which vie for authority in the field of human behaviour, namely, psychiatry and the law. In this article, I intend to analyse the interplay between these two disciplines within the arena of ‘crime and madness’, with a view to having a clear understanding of why the law in Ireland is as it is, and whether or not its position is apposite. Before commencing this examination, it is worth noting that the law and psychiatry both have the unenviable task of dealing with that most evasive entity, human behaviour. As a result, neither can ever achieve uniform perfection in their conclusions. This is not to say, however, that we should simply throw in our daggers and balances on the basis that we at least achieved a certain level of justice in terms of the psychiatric and legal treatment of mentally disordered offenders, but must use it to motivate ourselves to come as close as possible to a flexible, complementary relationship between the professions which will ultimately result in the most appropriate treatment for the accused.