The advantages of a monoblock design and lower cost have generated renewed interest in all-polyethylene tibial components for total knee arthroplasty (TKA). We hypothesized an all-polyethylene design would function equivalently to a metal-backed modular design at lower cost and at long-term followup. We report the 8- to 12-year followup of our earlier reported prospective randomized comparison of a modern congruent all-polyethylene tibial component with a modular metal-backed tibial component of the same design. The mean age of the patients was 69 years and 92% were diagnosed with osteoarthritis. Of 290 patients (316 total knee arthroplasties) enrolled, 120 patients died, 22 had revision surgery, and one was lost to followup. We followed the remaining 147 patients (167 TKAs: 97 all-polyethylene/70 metal-backed) clinically and radiographically. There were no differences in knee function (Knee Society clinical score, range of motion, stability) or radiographic parameters between the groups. Of the 22 revisions, only three were performed for tibial aseptic loosening (three metal-backed). Ten-year survivorship of the all-polyethylene tibial component was 91.6% with revision for any reason and 100% for aseptic loosening. The metal-backed tibial component survivorship was 88.9% with revision for any reason and 94.3% for aseptic loosening. The contemporary all-polyethylene tibial component functioned equivalently to its monoblock counterpart and was less costly.