Thirty-two multiple trauma patients with severe head injury and a Glasgow Coma Scale (GCS) score of 8 or less were prospectively studied to assess the occurrence of deep venous thrombosis (DVT) and pulmonary embolism (PE). All patients required mechanical ventilation. A sequential compression device (SCD) was used in 14 patients and 18 patients received no prophylaxis for thromboembolism. Bilateral lower extremity technetium venoscans and ventilation/perfusion (V/Q) lung scans were performed within 6 days of admission and every week for 1 month or until the patient developed DVT or PE or was discharged from the SCIU. Deep venous thrombosis occurred in two patients (6%) at 16 and 28 days following trauma. Twenty-five patients had normal or low probability V/Q scans. Six had high probability V/Q scans confirmed by pulmonary arteriograms (PAGs) at 12.5 ± 4 days. Clinical signs of PE were absent in all patients with a positive PAG. There were no differences in age, Injury Severity Score (ISS), GCS Score, APACHE II Score, or Trauma Score between the patients who developed DVT or PE and those who did not. A SCD was used in four of the eight patient with DVT or PE. All but one patient with DVT or PE underwent placement of a vena caval filter. Multiple trauma patients with severe head injury (GCS score ≤8) are at high risk for thromboembolism. The available means of prevention and diagnosis of DVT or PE in multiple trauma patients with severe head injury are not entirely effective.