Assessment is the foundation on which nursing care is delivered. The aim of this paper is to better understand the content (what information nurses seek about consumers) and the process (how they go about gathering that information) of a comprehensive mental health nursing assessment in practice. Using terms, such as 'nursing', 'mental health', and 'assessment', the CINAHL, Medline, and PsycINFO databases were searched for studies that describe the content and process of a comprehensive mental health nursing assessment. Although studies of aspects of mental health nursing assessment, such as the assessment of risk or carer burden, were found, no single study described both the content and process of a comprehensive mental health nursing assessment in practice. In Australia, a comprehensive assessment is codified as a competency to practice nursing; however, the standards of practice set for mental health nurses are less clear on what constitutes a comprehensive assessment or how this should be undertaken. The peer-reviewed literature describes assessment as both an independent and interdependent activity. It is described as informal, and there is evidence that comprehensive mental health nursing assessments are not well documented. The credibility of training and research into mental health nursing requires that the content and the process of a comprehensive mental health nursing assessment needs to be clearly defined.