The triage of patients in the hospital emergency department (ED) has developed as an efficient method to determine the level of urgency and provide appropriate care and treatment. The triage process has been found to be less effective for patients presenting with mental health related problems. Triage guidelines specifically tailored for mental health needs have been introduced in the attempt to overcome existing problems, however, the effectiveness of these guidelines has not been extensively tested. This paper presents the findings of a study conducted in a large metropolitan hospital in Melbourne, Australia. All presentations to the ED for psychiatric problems (n = 137) were triaged using the mental health guidelines over a 3-month period. The same presentations were triaged by psychiatric nurse consultants employed in the ED and the results compared. The results indicate a high level of difference in the triage ranking by the two groups of nurses, with emergency nurses tending to classify presentations as more urgent than their psychiatric nurse colleagues. These findings suggest that mental health education for emergency nurses is necessary if the guidelines are to be used effectively and improve outcomes for patients presenting with psychiatric problems.