Objective-To examine effects of an autologous platelet-rich fibrin (PRF) membrane for enhancing healing of a defect of the patellar tendon (PT) in dogs. Animals-8 adult dogs. Procedures-Defects were created in the central third of the PT in both hind limbs of each dog. An autologous PRF membrane was implanted in 1 defect/dog, and the contralateral defect was left empty. Dogs (n = 4/time period) were euthanized at 4 and 8 weeks after surgery, and tendon healing was assessed grossly and histologically via a semiquantitative scoring system. Cross-sectional area of the PTs was also compared. Results-Both treated and control defects were filled with repair tissue by 4 weeks. There was no significant difference in the histologic quality of the repair tissue between control and PRF membrane-treated defects at either time point. At both time points, the cross-sectional area of PRF membrane-treated tendons was significantly greater (at least 2.5-fold as great), compared with that of sham-treated tendons. At 4 weeks, the repair tissue consisted of disorganized proliferative fibrovascular tissue originating predominantly from the fat pad. By 8 weeks, the tissue was less cellular and slightly more organized in both groups. Conclusions and Clinical Relevance-A PRF membrane did not enhance the rate or quality of tendon healing in PT defects. However, it did increase the amount of repair tissue within and surrounding the defect. These results suggested that a PRF membrane may not be indicated for augmenting the repair of acutely injured tendons that are otherwise healthy.