At 07:39 on 11 March 2004, 10 terrorist bomb explosions occurred almost simultaneously in four commuter trains in Madrid, Spain, killing 177 people instantly and injuring more than 2000. There were 14 subsequent in-hospital deaths, bringing the ultimate death toll to 191. This report describes the organization of clinical management and patterns of injuries in casualties who were taken to the closest hospital, with an emphasis on the critically ill. A total of 312 patients were taken to the hospital and 91 patients were hospitalized, of whom 89 (28.5%) remained in hospital for longer than 24 hours. Sixty-two patients had only superficial bruises or emotional shock, but the remaining 250 patients had more severe injuries. Data on 243 of these 250 patients form the basis of this report. Tympanic perforation occurred in 41% of 243 victims with moderate-to-severe trauma, chest injuries in 40%, shrapnel wounds in 36%, fractures in 18%, first-degree or second-degree burns in 18%, eye lesions in 18%, head trauma in 12% and abdominal injuries in 5%. Between 08:00 and 17:00, 34 surgical interventions were performed in 32 patients. Twenty-nine casualties (12% of the total, or 32.5% of those hospitalized) were deemed to be in a critical condition, and two of these died within minutes of arrival. The other 27 survived to admission to intensive care units, and three of them died, bringing the critical mortality rate to 17.2% (5/29). The mean Injury Severity Score and Acute Physiology and Chronic Health Evaluation II scores for critically ill patients were 34 and 23, respectively. Among these critically ill patients, soft tissue and musculoskeletal injuries predominated in 85% of cases, ear blast injury was identified in 67% and blast lung injury was present in 63%. Fifty-two per cent suffered head trauma. Over-triage to the closest hospital probably occurred, and the time of the blasts proved to be crucial to the the adequacy of the medical and surgical response. The number of blast lung injuries seen is probably the largest reported by a single institution, and the critical mortality rate was reasonably low.