The aim of this review was to compare the reliability of existing triage scales. The research question was that, using kappa value as reliability measure, in adult ED patients to what extent did clinicians' triage ratings agree with eachother or with a gold standard? Methods: The search was limited to studies on adult patients (≥15 years) visiting EDs for somatic reasons and to English and Persian studies that have reported kappa. Studies solely on geriatric patients, computerized triage, telephone triage, and specialty triages were excluded. PubMed, Scopus, ISI web of knowledge, Mosby's Nursing Index, Magiran and SID, were systematically searched through August 2013. 13 articles for kappa (n=38829), 11 articles for linear weighted kappa (LWK) (n= 22697) and 12 articles for quadratic weighted kappa (QWK) (n=10915) met our inclusion criteria. Heterogeneity among studies and publication bias were checked. All pooled analyses of kappa scores for each triage scale were calculated based on random-effects model and then the scales were compared. Results: Findings suggest that five-level scales are more reliable in triaging patients in the emergency department than others (pooled kappa: 0.53, 95% CI (0.48, 0.57), LWK= 0.76, 95% CI (0.72, 0.81) and QWK = 0.74, 95% CI (0.69, 0.79)). The Canadian Triage and Acuity Scale (CTAS) and the Emergency Severity Index (ESI) have been studied more than the other scales. Conclusion: It seems necessary to set a consensus method to assess and compare the reliability of triage scales. This review suggests more specific studies on reliability of triage scales, especially on intra-rater agreement.