Introduction: Trauma team activation is a kind of triage the staff of an Emergency Department (ED) exerts to determine whether a trauma team needs to be activated for severely injured patients and in what composition the team needs to be deployed. It is a difficult decision-making process which is often performed by ED nurses and influenced by several factors. Objective: Understand the trauma team activation decision-making process at a Dutch ED and obtain insight in the importance of several factors of influence according to ED nurses. Methods: Cross-sectional fractional factorial design. Patient factors (attributes) were identified by literature review and discussed with trauma experts. SPSS® Orthoplan was used to generate a fraction (n=25) of all possible alternative scenarios (n=2304), that consisted of combinations of the attribute levels. Scenarios were presented to 44 ED nurses at a level I trauma centre using a questionnaire with a total of 26 clinical vignettes. ED nurses were asked to rank the attributes according to their perceived importance. Results: 27 ED nurses (61%) completed the questionnaire. The number of team activations per respondent varied for the possible teams. After normalizing the level mean rank scores, the level Airway-Breathing unstable was the most important level for trauma team activation based on the relative rank sum weight (0.115), followed by Mechanism of injury Fall of height >5m (0.171) and Airway-Breathing Intubation (0.172). There was no difference in attribute mean rank scores between two groups of ED nurses, stratified for years of work experience. The ICC for the different levels occurring in the three duplicate vignettes varied. Discussion: We observed variation in decisions for trauma team activation and in consistency of the rank scores among the ED nurses under study. This implies that a decision support system could improve uniformity in the trauma team activation decision-making process.