The criminal laws of all legal systems around the world recognise a defence of insanity in some form. In Bhutan, s 119 of our Penal Code provides defendants with a defence, who were mentally impaired at the time they committed the offence charged. This article comprises a critical appraisal of s 119, in the form of an examination of its elements and application in practice. In this exercise, we shall consider the equivalent defence in some other legal systems as a means of evaluating the strengths and weaknesses of our own defence. In particular, since s 119 was borrowed directly from the US Model Penal Code, it will be pertinent to consider what commentators have said about that Code’s provision.