Undetected lower-extremity deep-vein thrombosis (LEDVT) in the trauma patient can lead to significant morbidity and mortality. The purpose of this study was to: 1) evaluate the role of ultrasonography in the early detection of LEDVT in high-risk trauma patients; 2) identify prognostic indicators that predict LEDVT; and 3) evaluate the efficacy of selected inferior vena cava (IVC) filter placement in the prevention of pulmonary emboli. From October 1993 through December 1994, all adult multiple-trauma patients admitted to the Trauma Service who required prolonged bed rest (>3 days) or sustained a lower-extremity, pelvic, or spinal fracture with paralysis were prospectively studied with serial physical examinations and lower-extremity venous ultrasounds within 72 hours of admission and then weekly until discharge. Two hundred twenty-eight patients were entered into the study. Thirty-nine patients (17%) developed ultrasound evidence of LEDVT; of these, only seven (18%) were evident on physical examination. This allowed 32 patients (82%) with unsuspected LEDVT to receive earlier definitive therapy. Multivariate logistic regression analysis of LEDVT with various predictors found age, hospital length of stay, and lower-extremity trauma to be significant predictors of LEDVT (P < 0.05). Twenty-nine patients (74%) had immediate IVC filter placement upon ultrasound identification of proximal LEDVT. None of these patients developed pulmonary emboli. Ten patients (26%) with a LEDVT were treated with systemic anticoagulation alone. One of these patients sustained a fatal pulmonary embolus. In a historic control group of 234 high-risk trauma patients admitted in the 14 months prior to implementing screening ultrasounds, six patients sustained pulmonary emboli (P < 0.05). Screening ultrasounds combined with selective placement of IVC filters play an important role in reducing the morbidity and mortality associated with LEDVT in high-risk trauma patients.