Emergency Departments (EDs) across Italy use different triage systems, which vary from region to region. This study aimed to assess whether nurses working in different EDs assign triage codes in a similar and standardized manner. A multicenter observational simulation study involved the EDs of Bolzano Hospital, Merano Hospital, Pisa University Hospital, and Rovereto Hospital. All participating nurses were given 30 simulated clinical cases (vignettes) and asked to assign triage codes according to the triage systems used in their EDs. Subsequently, we assessed inter-rater agreement and evaluated if code assignment had different performance among hospitals in relation to different clinical outcomes. Eighty-seven nurses participated in this study. There was marked variation in assigned triage codes both across hospitals and among individual operators. The kappa values for inter-rater agreement were 0.632 for Bolzano Hospital, 0.589 for Merano Hospital, 0.464 for Pisa University Hospital, and 0.574 for Rovereto Hospital. Sensitivity and specificity levels varied considerably for the same outcomes when comparing different hospitals. There is a high degree of subjectivity in triage code assignment by ED nurses. In the interest of equitable care for patients, this variability within the same country is hardly acceptable.