Bilateral total knee replacements were reviewed to determine whether any difference exists in the perioperative course between procedures done under one anesthetic (simultaneous) and those done under two anesthetics (staged). There were 29 staged and 18 simultaneous cases, therefore 76 separate procedures and 94 knees done. The total operative time, blood loss, and complications were similar between the two groups. However, the staged replacements had more than twice the hospital days (34.6 +/- 7.7 vs. 16.8 +/- 5.6, P less than .001) and 18% greater hospital bills. In fact, for a given patient, the hospital bill may be greater than 50% higher if a staged rather than simultaneous replacement is done. Therefore, simultaneous replacement is recommended for appropriate patients.