AIMS AND OBJECTIVES:To evaluate the effect of a stop smoking clinic on the quit rates of patients admitted to an acute in-patient unit. BACKGROUND:The relationship between poor physical health and severe mental illness is well established. High rates of smoking appear to play an important causal role in the excess morbidity and mortality in this population. Stop smoking interventions for the general population are clinically effective and cost-effective. There is a small but promising evidence base for effective interventions to help people with a mental illness who wish to stop smoking but these have mostly been tested with community patients rather than acute in-patients. METHODS:A service evaluation of a drop-in stop smoking clinic on an acute mental health in-patient unit was conducted. Patients' smoking status was measured at baseline and four weeks after their quit date using patient self-report and an expired breath carbon monoxide reading. RESULTS:Over a six-month evaluation period, 46 patients set a quit date and 13 (28·3%) were abstinent at the four-week follow-up stage, verified by a carbon monoxide reading (χ(2) =33, df=1, sig p<0·0001). CONCLUSIONS:This small-scale evaluation has shown a drop-in stop smoking intervention to be feasible, acceptable and associated with positive outcomes; further research with larger, more representative samples is required. RELEVANCE TO CLINICAL PRACTICE:Enforcing smoke-free legislation is a contentious issue on mental health in-patient units, and there is a paucity of research to guide nursing practice in this area. An admission period in a smoke-free environment provides a crucial opportunity to offer smoking cessation treatment. With appropriate resources, expertise and support, it appears possible to apply smoking cessation interventions that are successful within the general population to mental health patients during an acute admission.