Clear role definition is essential for directing the focus of nurse education and several studies have attempted to define the role of the mental health nurse (MHN). These, however, came to the conclusion that mental health nursing was difficult to articulate. The aim of this study was to understand how, during their transition to first level registration, mental health student nurses (MHSNs) perceived the role of the MHN. Semi-structured interviews were conducted with 14 MHSNs during the last 6 months of their transition to MHN. Transcripts were analysed using a qualitative approach based on grounded theory. Six key themes were identified, five of which were defined mental health nursing roles. The sixth theme related to non-therapeutic intervention on the part of some MHNs. Several areas of concern were identified. First, MHSNs expected to conduct more psychologically based interventions than were achievable in practice. Second, emphasis on drug administration can lead to a conflict of interest in the nurses’ advocacy role with patients. Third, MHSNs sometimes observed poor role models in their placements, which could have a negative impact on the way in which future MHNs view the role of the MHN.