75 patients with isolated non-traumatic tibiofemoral cartilage degeneration were randomized to receive an intra-articular injection of either platelet-rich plasma (PRP) or 1% mesocaine (control). Injection protocol consisted of 6 weekly injections, followed by 3 months of no injections, and then subsequently re-continued with 3 additional single injections administered at 3 month intervals. The purpose of this study was to determine the effect of PRP on cartilage regeneration and knee function at 1 year after the conclusion of treatment. The PRP group displayed significant improvements in knee function outcomes (Lysholm, IKDC, Cincinnati scores) and the control group did not display any improvements, at 1 year. No between-group comparisons were made with respect to knee function outcomes, and the PRP group did not see a significant change in cartilage thickness.