We describe and analyze the response of the emergency department (ED) to the events of 11 March, 2004. The ED played a major role in the care of victims who survived the initial explosions. Of the 976 victims transferred to hospital that day, 325 (32%) were attended in the ED of the Gregorio Maranon University Hospital. Nine percent were critically ill and only 5 died. The first step was to evaluate and transfer the 123 patients who were already in the ED when the explosions took place, thus freeing the emergency area. Victim triage was organized in three stages: external triage, triage in the ED, and a third triage in the critical care unit. The emergency areas were reclassified into resuscitation, major trauma and minor trauma. There were no staff shortages as personnel spontaneously volunteered. Finally, the main factors related to the success of the interventions, as well as the deficiencies found, are discussed.