Bilateral total knee replacements during a single operation with intramedullary femoral guide rods have been associated with the possible development of a fat embolism syndrome. To assess the safety of this procedure, in which the femoral canal was decompressed by the use of an overdrilled entrance hole and fluted guide rod, 17 unilateral and 18 bilateral consecutive total knee patients were evaluated. There were no differences between the groups on the basis of changes in chest radiographs, percentage of estimated pulmonary shunting, mental status changes, or fat and bone marrow elements drawn from a central venous catheter in the right atrium. Although no patient had free fat in the blood, bone marrow elements were found in 3 bilateral and 2 unilateral cases. No patient had clinical manifestations of a fat emboli syndrome. With appropriate femoral canal decompression, bilateral 1-stage total knee replacement appears to be a safe procedure.