A role in any human institution is a mixture of objective reality together with phantastical images from unconscious and defensive sources. I shall illustrate some of these roles in the mental hospital from my own experience; and I shall argue that the psychotherapist has a significant place in this unconscious phantasy system, which it is important for us, as psychoanalysts working in the National Health Service, to know about and to understand. I suggest, too, that these pressures act upon us all whether we work in large mental hospitals or elsewhere as psychotherapists. The theory of social defence systems is used as a framework for understanding the processes in our own institutions. This paper is an attempt to show how helpful this psychoanalytical theory of institutions is for our practice in the NHS.