Although few trauma patients sustain fatal pulmonary embolism, a large population is at risk from nonfatal embolism due to unrecognized deep vein thrombosis (DVT). Thirty-eight of 39 immobilized trauma patients at bed rest for 10 days or longer had venographic study of their lower extremities to evaluate for the presence of silent DVT. Sixty percent of patients had silent DVT, with thrombi extending above the knee in half the patients with clot. DVT was documented in 67 percent of patients with major lower extremity fractures and 59 percent of patients without major fractures. DVT increased with increasing age but not with injury severity score.