Pathologic thrombosis, in the form of pulmonary embolism (PE) and deep venous thrombosis (DVT), causes significant morbidity and mortality in trauma patients and presents a diagnostic and therapeutic challenge because of associated conditions in these patients. This study examines the measurement of D-dimer crosslinked fibrin degradation products (D-dimer XDPs) as an indicator of hypercoagulability that places a trauma patient at risk of developing pathologic thrombosis. The time course of changes in D-dimer values after trauma normally involves an initial increase with a rapid decrease of D-dimer XDP levels to normal. Patients who then demonstrate a second rise in D-dimer values are at risk for pathologic thrombosis. Forty-one trauma patients were studied, in two groups, to evaluate the potential use of D-dimer XDP levels in evaluating the risk of pathologic thrombosis. A secondary increase in D-dimer XDP levels was found to occur in patients with PE, although sepsis and adult respiratory distress syndrome can also cause a late increase. However, D-dimer determinations appear to provide an easy, relatively inexpensive means of evaluating trauma patients for the risk of pathologic thrombosis.