Older people are at risk for developing psychiatric disorders and require highly skilled and knowledgeable nurse practitioners to provide early recognition and intervention of psychiatric problems. This study sought to identify the aged care mental health knowledge of registered nurses (RNs) employed in long-term aged care and test the validity and reliability of a North American tool for use in an Australian context. The Mary Starke Harper Ageing Knowledge Exam (MSHAKE) was sent to RNs (n = 350) in 70 long-term care facilities (LTCF) in Queensland, Australia, and 107 surveys were returned (30.5% response). Participants were found to be unprepared for the reality of caring for the mental health needs of an older population and to have knowledge deficits related to suicide, prevalence of mental illness, mental health and ethnicity, and a number of issues regarding dementia.