Venous thromboembolism, which includes both deep vein thrombosis (DVT) and pulmonary embolism (PE), is a common complication after injury. PE carries a mortality rate of 11% and is the third leading cause of death after injury. Traditionally, PE has been thought to originate from a clot in the lower extremities or vena cava that migrates to the lungs. However, with the liberal use of computed tomography after injury, many small thrombi (pulmonary thrombi or PT) are being found in the pulmonary arteries that may be de novo clots that arise due to pulmonary injury or inflamation. This novel finding has major implications for both prophylaxis and treatment. The CLOTT study group that includes 17 investigators from 17 major trauma centers could not come to a consensus as to the treatment of asymptomatic PT. This prospective observational multicenter study will collect data from seriously injured patients who develope PE/PT admitted to any of our 17 trauma centers without altering the standard of care at any center allowing us to compare two treatment patterns: anticoagulation versus observation. If this study supports our hypothesis that occult PT do not need specific treatment, it would have a major impact on practice patterns and would prevent overtreatment in a large number of injured patients.