Aim. In this paper we report on the rates of drug/alcohol use on acute psychiatric wards in relation to levels and intensity of exit security measures. Background. Many inpatient wards have become permanently locked, with staff concerned about the risk of patients leaving the ward and harming themselves or others, and of people bringing illicit substances into the therapeutic environment. Methods. In 2004/2005, a cross sectional survey on 136 acute psychiatric wards across three areas of England was undertaken. A comprehensive range of data including door locking and drug/alcohol use were collected over 6months on each ward. In 2006, supplementary data on door locking and exit security were collected. Door locking, additional exit security measures and substance misuse rates of the 136 wards were analysed and the associations between these were investigated. Results. No consistent relationships were found with exit security features, intensity of drug/alcohol monitoring procedures, or the locking of the ward door. There were indications that use of breath testing for alcohol might reduce usage and that the use of 'sniffer' dogs was associated with greater alcohol use. Conclusion. Greater exit security or locking of the ward door had no influence on rates of use of alcohol or illicit drugs by inpatients and thus cannot form part of any strategy to control substance use by inpatients. There are some grounds to believe that a greater use of screening might help reduce the frequency of alcohol/substance use on wards and may lead to a reduction in verbal abuse.