A 26-year-old man manifested clinical signs of a left iliofemoral thrombosis 12 weeks after closed head injury in a motor vehicle accident. The deep vein thrombosis was initially diagnosed by venography and appropriate anticoagulation therapy was instituted. After four days of treatment, there was no significant resolution of signs or symptoms and the circumference of the left thigh had increased with an associated decrease in hemoglobin. A CT scan of the involved thigh revealed hemorrhage and calcification within the quadriceps muscle. In retrospect, it was evident that the hemorrhage and heterotopic ossification had caused compression of the surrounding tissue and vessels thus mimicking a deep vein thrombosis on venography. Clinicians need to be aware of the similarity of the early clinical manifestations of heterotopic ossifications and deep vein thrombosis and the complications which could arise with anticoagulation therapy initiated too early in the course of the disease.