Aims and objective: To capture the experiences of nurses in relation to the acutely physiologically deteriorating consumer. Background: Improving the physical health care of consumers with mental illness has been widely adopted as a priority for mental health nursing. Much of the effort thus far has focused on routine screening, prevention and treatment of common comorbidities including cardiovascular disease, diabetes mellitus and cancer. There has been less focus on the acutely physiologically deteriorating consumer in the mental health setting. Further study is warranted since this issue poses a set of highly complex challenges for nurses within the inpatient setting. Method: An exploratory, descriptive study was employed using focus groups to gather narrative data, which was then subject to qualitative analysis. Eleven mental health inpatient wards within a local health district in Sydney, Australia, were studied, comprising ward-based nurses (n = 64) and nurse unit managers (n = 8). This paper follows the COREQ guidelines for reporting qualitative health research. Results: Qualitative data analysis revealed three themes central to the nurses' experience: (a) lack of clarity (subthemes: procedures and leadership accountability); (b) confidence in the workforce (subthemes: knowledge and skills, training needs, relevant experience, collaboration with emergency and medical teams, stigmatising attitudes); and (c) complexity (subthemes: complexity as the new norm and suitability of the mental health environment). Conclusion: The themes found in this study can be used to guide and inform healthcare policy, protocols, education and processes around building a more confident nurse workforce for the acutely physiologically deteriorating consumer. Relevance to clinical practice: Findings provide a rich data set for the generation of measurement tools and protocols to guide physical health care and evaluate performance.