Objective: To measure environmental tobacco smoke (ETS) exposure in psychiatric settings and to assess determinants of support for complete smoking bans. Design: Cross sectional study Setting: Dutch psychiatric hospitals, outpatient care institutions, and sheltered home facilities. Subjects: A random sample of 540 treatment staff, 306 attendants/nurses, and 93 patients. Main outcome measures: Self reported ETS exposure, current smoking policy, compliance with smoking policy, beliefs about smoking bans. Results: 87% of respondents were exposed to tobacco smoke in psychiatric institutions; 29% said that on an average day they were exposed to ''a lot of smoke''. Although ETS originates mainly from smoking patients, both non-compliance from patients and employees with existing bans resulted in non-smokers being exposed to ETS. Due to non-compliance, ETS exposure was quite high when there is a general smoking ban (designated areas option). Only with a complete ban was compliance good and employees sufficiently protected from ETS exposure. Psychiatrists, psychologists, physicians, attendants, and nurses were most concerned about resistance from patients, partly because of the fear of infringing on patients' freedom to smoke. Conclusions: Complete smoking bans are the only way to fully protect those working in psychiatry from ETS exposure, mainly because general smoking bans are not sufficiently complied with. Communication strategies to improve compliance with complete bans are crucial to protect those working in psychiatry from ETS. Compliance could be improved by addressing the belief that the ban will effectively result in less ETS exposure and the issue of patients' freedom to smoke versus employees' right to work in a smoke-free environment.