The existing evidence on the effectiveness of thromboprophylaxis after trauma is conflicting. Although prophylaxis with heparin and/or sequential compression devices is practiced widely, many studies failed to document a clear benefit. A recent meta-analysis suggests that prophylaxis does not reduce posttraumatic deep venous thrombosis rates compared to no prophylaxis. The objective of this prospective study is to examine if the use of thromboprophylaxis prevents posttraumatic pulmonary embolism (PE). Sixty-four critically injured patients with clinical evidence of PE were studied by computed tomographic pulmonary angiography and/or conventional pulmonary angiography. PE was diagnosed in 24 (37.5%) patients. Patients with PE were similar to patients without PE with regard to demographics, injury type and severity, operations, and mortality. Thromboprophylaxis was used with equal frequency between PE and no-PE patients (71% vs 80%, P = 0.4). The type of prophylaxis used was similar between patients with PE (17% heparin, 71% sequential compression devices, 17% combination) and patients without PE (32%, 57%, and 10%, respectively; P = 0.16, 0.28, 0.69, respectively). Current methods of posttraumatic thromboprophylaxis may be inadequate. Practices from nontrauma populations have been erroneously extrapolated to the unique trauma population. To reduce the rate of PE after trauma, new methods of thromboprophylaxis should be considered.