Objectives: US soldiers suffer catastrophic injuries during combat. We sought to defi ne risk factors and rates for VTE in this population. Methods: We gathered data each hospital day on all patients injured in Afghanistan or Iraq who were admitted to the Walter Reed Army Medical Center (WRAMC). We analyzed prophylaxis rates and effi cacy and identifi ed risk factors for VTE. Results: We recorded data on 506 combat casualties directly admitted to WRAMC after medical air evacuation. The average injury severity score for the group was 18.4 ± 11.7, and the most common reason for air evacuation was injury by improvised explosive device (65%). As part of the initial resuscitation, patients received 4.7 ± 9.0 and 4.00 ± 7.8 units of packed RBCs and fresh frozen plasma, respectively, and 42 patients received factor VIIa. Forty-six patients (9.1%) were given a diagnosis of VTE prior to discharge, 18 (3.6%) during air evacuation, and 28 (5.5%) during the hospital stay. In Cox regression analysis, administration of 1 unit of packed RBCs was associated with a hazard ratio (HR) of 1.04 (95% CI, 1.02-1.07; P = .002), and enoxaparin, 30 mg bid, administered subcutaneously for the majority of hospital days was associated with a HR of 0.31 (95% CI, 0.11-0.86; P = .02) for VTE during the hospitalization. Conclusions: Patients who suffer traumatic injuries in combat overseas are at high risk for VTE during evacuation and recovery. Those with large resuscitations are at particularly high risk, and lowmolecular-weight heparin is associated with a decrease in VTE.