The UK Department of Health required that by April 2001, all NHS bodies would have implemented a smoking policy. It has been suggested that the best demonstration a hospital can make of its commitment to health is to ban smoking on its premises. This paper reports on an evaluation of the effectiveness of a non-smoking policy in a newly opened NHS psychiatric hospital. Questionnaires were sent to all 156 nursing staff in a psychiatric hospital to assess the effectiveness of the policy in terms of staff smoking behaviour, attitudes to the restriction and compliance with the policy. Of the 156 questionnaires distributed, 92 (58%) were returned; smokers, former smokers and those who have never smoked were quite evenly represented at 34.78%, 34.78% and 30.43%, respectively. Of eight critical success factors for the policy, only one, staff not smoking in Trust public areas, had been achieved. A non-smoking policy was generally accepted as necessary by nursing staff working in a mental health setting. Staff felt that the policy was not effective in motivating smoking nurses to stop and that insufficient support was given to these nurses. The study highlights the importance of introducing staff support systems as an integral part of smoking policies and the role of counterintuitive behaviour in the effectiveness of smoking policy introduction in healthcare settings.