One hundred consecutive patients with multiple trauma, who were admitted to a level I trauma center with an injury severity score of 10 or greater, were studied prospectively. A duplex scan was used to evaluate each patient initially and at set intervals during the hospitalization for the presence of deep vein thrombosis (DVT). The prophylactic regimen for DVT in this study was 5,000 U of subcutaneous heparin every 12 hours. This was used in 50 patients at the discretion of the attending physician, while the remaining 50 patients received no DVT prophylaxis. Fourteen of 50 patients (28%) who were receiving heparin developed DVT, while only 1 patient (2%) of the 50 who did not receive heparin developed DVT. The use of heparin did not provide any significant protection in the susceptible trauma patient. It is believed that those patients with minimal lower extremity injuries, lower injury severity scores, and a shorter period of immobilization do not require any form of DVT prophylaxis. However, those patients at increased risk for DVT are better served with either increased doses of heparin or alternative forms of DVT prophylaxis.