This paper describes the evaluation of a computerized clinical decision support system (CCDSS) for Emergency Department (ED) triage. The CCDSS for triage was developed as a means to improve ED quality and safety. Whilst there is significant research on the role of CCDSS in health care, their role in EDs remains under-investigated. In this study, a CCDSS for ED triage was developed and evaluated using a quasi-experimental interrupted time-series design. Data was collected at four time points before and after the introduction of the CCDSS to assess key aspects of quality and safety within the ED. The results demonstrated a statistically significant improvement in triage prioritization (p < 0.001), pain scoring (p < 0.001) and pain management (p < 0.001). This study clearly identifies the positive clinical impact that a CCDSS can have on quality and safety for ED patients and provides a unique contribution to the current knowledge base.