176 patients were randomized to determine the efficacy of three intra-articular injections of plasma rich in growth factors (PRGF) versus hyaluronic acid (HA) injections in the treatment of symptomatic knee osteoarthritis. Clinical outcome using the Western Ontario McMaster Universities Osteoarthritis Index (WOMAC) was measured over 6 months. The results indicated that a greater percentage of patients treated with the platelet-rich plasma (PRP) product experienced at least a 50% reduction in pain, however mean WOMAC pain, stiffness and function subscale scores did not significantly differ between treatments.