This study investigates the interrater reliability and the accuracy of Manchester Triage (MTS) at emergency departments in Western Sweden. Methods: A group of 79 nurses from seven emergency departments assessed simulated patient cases and assigned triage categories using the same principles as in their daily work. K statistics, accuracy, over-triage and under-triage were then analyzed. The nurses performed 1027 triage assessments. Results: The result showed an unweighted κ value of 0.61, a linear weighted κ value of 0.71, and a quadratic weighted κ value of 0.81. The determined accuracy was 92% and 91% for the two most urgent categories, but significantly lower for the less urgent categories. Conclusions: Patients in need of urgent care were identified in more than nine out of 10 cases. The high level of over-triage and under-triage in the less urgent categories resulted in low agreement and accuracy. This may suggest that the resources of emergency departments can be overused for non-urgent patients.