“Unfitness to plead” is a medico-legal proposition of practical importance to prison medical officers. My attention was drawn to it, shortly after I joined the Service, in a case tried at the Central Criminal Court. Since then I have frequently had to take the responsibility of forming an opinion and reporting as to prisoners' fitness or unfitness to plead, and recently my interest in this problem has been re-aroused by a case tried at the Manchester Assizes, the outcome of which I had discussed with my colleagues and also with members of the Bar.