This paper presents the findings from a study undertaken to describe nursing practice in one dual diagnosis (DD; coexisting mental illness and intellectual disability) inpatient unit in New Zealand. A focused ethnographic approach (using fieldwork observations, a review of documents, and five semistructured interviews) was used to gather data. A model of culture was used to analyze data to allow a description of DD nursing practice. Additionally, this framework allowed for an exploration of the artefacts, values, and assumptions that underpin these practices. Three key themes emerged from the data: keeping everyone safe, managing the complexities in assessment, and narrating their work. Together, these themes indicate that in the absence of a defined model of DD nursing, practice is based on an institutional psychiatric model. We argue that DD nursing models need to be made explicit in order to advance nursing in this area.