Current research is investigating new methods for stimulating repair or replacing damaged cartilage. In particular, the most recent knowledge regarding tissue biology highlights a complex regulation of growth factors (GFs) for the normal tissue structure and the reaction to tissue damage. The influence of GFs on cartilage repair is now widely investigated in vitro and in vivo. Platelet Rich Plasma (PRP) is a simple, low- cost and minimally- invasive method that allows one to obtain a natural concentrate of autologous GFs from the blood, and it is increasingly applied in the clinical practice to treat knee degenerative pathology, such as chondropathy and early OA. The biological rational of PRP is that platelets contain storage pools of GFs, cytokines, chemokines and many other mediators.Although its widespread application, there are no high level studies in the literature to demonstrate the real efficacy of PRP. In fact, at the present moment, to our knowledge there is no published randomized controlled trial comparing PRP with other conservative treatments commonly used for knee OA.