this is the first canadian study to examine acute care mental health nurses' adherence to clinician-level (4a protocol) and systems-level recommendations from the registered nurses association of ontario's best practice guidelines (2007). this study also examined respondents' beliefs, confidence, and perceived facilitators and barriers. persons with a mental illness can and want to quit smoking but have higher tobacco use prevalence and quit at lower rates than do smokers in the general population. psychiatric nurses are well positioned to intervene given their daily one-on-one patient contact. a questionnaire was mailed (in three steps) to 141 registered nurses who provide care to mental health inpatients within two northern ontario regions. over three-quarters of respondents performed at least one of the strategies listed within each step of the 4a protocol ( ask, advise, assist, arrange ) but strategies were performed between 'seldom' and 'occasionally' and few (6%) spent more than the recommended 10 minutes or more for persons with a mental health disorder. patient motivation was both the biggest barrier and facilitator to intervening. a general lack of systems-level strategies was identified, few had received tobacco cessation training, and only 19% had seen the rnao guidelines. however, the majority had high confidence and positive beliefs about intervening, felt intervening was 'somewhat' part of their role, and expressed interest in further training. the findings suggest that improvements are needed to increase the frequency of intervention and amount of time spent intervening. psychiatric inpatient facilities could playa key role towards supporting nurses to meet their patients' tobacco cessation needs and help reduce this patient populations' disproportionately high smoking prevalence.