Objectives To describe and compare characteristics, care delivered, and outcomes of patients who presented to an emergency department (ED) with a mental health illness before and after the implementation of a patient flow strategy. Methods This was a retrospective, descriptive study. Health care data of patients who presented to a public teaching hospital ED in Queensland, Australia diagnosed with a mental health illness before (5th September 2011-4th March 2012) and after (5th March 2012-4th September 2012) the implementation of a patient flow strategy were analysed. Results A total of 3037 (before: n?=?1511; after: n?=?1526) mental health presentations (4.5% of all ED presentations) were made to the ED. Following the implementation of a patient flow strategy, improvements in ED length of stay, tests performed and nursing observations were seen. These varied by mental health diagnosis. Conclusion Our results indicate that a targeted approach to improving service delivery for a specific cohort of ED patients can make a difference without additional staffing. Further focused refinement of the strategy (such as time waiting for treatment) may be required.