- Background Conducting a thorough after-action review (AAR) process is an important component in improving preparedness for mass casualty incidents (MCIs). Purposes The study aimed to develop a structured AAR tool for use by medical teams in emergency departments after an MCI and to identify the best possible procedure for its conduct. Basic procedures On the basis of knowledge acquired from an extensive literature review, a structured tool for conducting an AAR in the emergency department was developed. A modified Delphi process was conducted to achieve content validity of the tool, involving 48 medical professionals from all 6 level I trauma centers in Israel. The AAR tool was tested during a simulated MCI drill. Main findings All experts support the conduct of an AAR in the ED after an MCI to build and maintain capacity for an adequate emergency response. More than 80% agreement was achieved regarding 14 components that were implemented in the proposed AAR tool. Ninety-four percent perceived that AARs should be conducted within 24 hours from the event using both written reports and face-to-face discussions. Both physicians and nurses should participate. The incident manager should lead the AAR, limiting the time allocated for each speaker and for the AAR in whole. Principle conclusions Conducting a structured AAR in all emergency departments after an MCI facilitates both learning lessons regarding the function of the medical staff and ventilation of feelings, thus mitigating anxieties and expediting a speedy return to normalcy.