A brief review of the historical background of psychiatric treat-ment in England and Wales, followed by suggested architectural needs for a psychiatric unit in a general hospital. There is a plea for help in designing studies to evaluate the advantages and disadvantages of mental and general hospital milieux. I would like to discuss the problem of the appropriate environment for the treatment of psychiatric illness. My experience is confined to the situation in England and Wales and my remarks will refer to my personal knowledge. I have no reason to believe that the situation is very different in other countries, although there are minor variations. I think it important to set the problem in context by giving a brief historical account of the background to the present situation.