The range of motion, the stability of the knee, and the prevalence of radiolucent lines in 68 posterior cruciate-retaining (CR) total knee arthroplasties (TKAs) with a retained, but balanced, posterior cruciate ligament were compared with those in 68 knees with a posterior cruciate-substituting (PS) TKAs in the 60 patients who were managed with simultaneous bilateral TKAs. The average range of motion in both groups (126 degrees vs 129 degrees) at the latest follow-up was not significantly different (P = .359). No significant difference in the sagittal laxity of the knee was seen between 2 groups. The prevalence of radiolucent lines was 7% in the CR TKA with a recession posterior cruciate ligament and 12% in the PS TKA group (P = .108). We feel that posterior stabilization is unnecessary in the PS flex knees.