Fat embolism after bilateral total knee arthroplasty (TKA) occurred in 12% of the authors' patients having bilateral TKA with intramedullary instrumentation. Usually embolism was manifested as neurologic changes, most often changes of mental status. Death is a potential consequence, and this occurred in one patient. The present authors believe that fat embolism is not predictable preoperatively and propose that intraoperative guidelines can be used to reduce risk of this complication. Intraoperative monitoring by a Swan-Ganz catheter will permit measurement of the pulmonary arterial pressure, pulmonary vascular resistance, and pulmonary capillary wedge pressure. A sustained rise of any of these would be an indication to abort the second knee operation. If Swan-Ganz catheter is not available, a sustained fall of oxygen saturation to 90% or lower can be used as a criterion. The risk for fat embolism is increased with the use of intramedullary instrumentation, and the above guidelines are recommended for operations with this type of instrumentation. A fluted intramedullary rod and vent holes should be used.