Eighty-six consecutive patients undergoing spinal surgery were studied with preoperative and postoperative compression ultrasonography of the lower extremities to identify acute deep venous thrombosis. Compression stockings were the only method of prophylaxis. Postoperative deep venous thrombosis developed in five patients (6%). Serial ultrasound scanning revealed propagation of the thrombus proximal to the knee in one patient, who was the only patient to be anticoagulated. There were no statistically significant differences in the incidence of deep venous thrombosis compared to the type of procedure, age, sex, length of operation, or duration of bed rest. In conclusion, deep venous thrombosis distal to the inguinal ligament is unusual after spinal surgery. Given the potential complications of anticoagulation, we recommend only mechanical prophylaxis.