Background: There have been several histological studies of the Leeds-Keio ligament in anterior cruciate ligament reconstruction, but there have been few of the Leeds-Keio ligament in the extra-articular portion. Aims/Methods: To report the histological and ultrastructural findings of two cases of medial patellofemoral ligament reconstruction using the Leeds-Keio ligament, removed 6.1 years and 8.7 years after implantation. Results: In both cases, the tissue over the Leeds-Keio ligament was a ligament-like tissue. Electron microscopy showed that the diameter of the collagen fibrils in the tissue over the Leeds-Keio ligament was unimodal in the case investigated 6.1 years after implantation but bimodal in the case investigated after 8.7 years. Conclusions: The tissue over the Leeds-Keio ligament may continue to grow with prolonged periods of mechanical stress.