In this paper two major problem fields regarding the functionality of buildings for healthcare are indentified as 'high tech' versus 'low tech' and incongruity between intended functions and allocated space. Examples are drawn from post occupancy evaluations peformed in buildings of this type. The dual problem of future operational usage and design specifications that adequately mirror future use will be clarified and discussed from the viewpoint of functional safety of systems. It seems that evaluation of existing facilities as a form of feedback for the design of new facilities has to be accompanied by 'feedforward' design methods which permit the designer to maximise functionality and built-in flexibility.