Patients undergoing bilateral simultaneous total knee arthroplasty experienced early supported-weight-bearing on both knees. They were compared with two similar groups of patients whose postoperative weight-bearing on the operated extremity was markedly restricted. The clinical results and incidence of complications were similar in the three groups. There were no significant differences in the incidence of radiolucent lines at follow-up examination two to five years later. Bilateral simultaneous total knee arthroplasty is an effective and safe method of managing patients with arthritic knees where both require replacement. Early supported bilateral weight-bearing does not appear to have any deleterious effects on the bone-cement interface that can be detected on clinical or radiographic analysis. However, all patients should not be considered for bilateral prosthetic knee arthroplasty simply because they have arthritic changes in both knees and the procedure is efficacious. Frequently, only one knee is significantly painful or deformed, and its correction may relieve the opposite knee for an extended period. Bilateral operations are indicated when the pain and deformity of an unoperated knee will significantly retard the reconstructed knee, as in severe flexion contractures or malalignment.