Abstract. - We report the case of a 50 yearsold man who complained persisting knee pain that limited almost completely his sport performance. Since he previously underwent multiple aortocoronaric by-passes, he presented a chronic anti-aggregant therapy. In spite of this clinical history, he was still sport active and able to run long-distance races, until knee symptoms limited is activity level. Conservative treatment approaches proved to be unsuccessful, thus we decided to treat him by 3 Plateletrich Plasma (PRP) injections even if chronic anti-aggregant therapy is generally regarded as a contra-indication for PRP, since this kind of drugs impairs platelet function and granules\'\nrelease. Despite these premises, the clinical outcome was very satisfactory and the patient was able to rapidly resume intensive running activity. This experience opens new questions regarding the real potential of PRP in treating degenerative musculo-skeletal disorders, and in particular on its range of biological actions and on its limitations for clinical application.