RESEARCH GOAL. To examine PRP's effectiveness in reducing the pain of patients with knee osteoarthritis by comparing pain levels before and after intraarticular outpatient treatment of PRP. The efficacy is determined by the decrease in pain intensity the according to the VAS pain scale. STUDY STRUCTURE. The conducted research is a cross-sectional study of patients with knee osteoarthritis treated at the Department of Orthopedics and Traumatology, Clinical Hospital Center Osijek. PARTICIPANTS AND METHODS. The study included 36 patients with knee osteoarthritis treated at the Department of Orthopedics and Traumatology, Clinical Hospital Center Osijek, with the PRP application to the knee joint at periodic intervals of two applications within a month. The data used was from the existing medical records of patients treated during the previous three months by outpatient treatment of PRP to the knee joint due to its degenerative changes. The Kellgren-Lawrence classification was used to determine the degree of arthrosis. RESULTS. The study shows that in patients with grade III knee osteoarthritis, the pain is significantly severer than in subjects with grade II and I knee osteoarthritis. After the first intraarticular PRP application, there is a significant decrease in the amount of pain according to the VAS pain scale in the observed age groups. Patients who are older than 55 have the most significant reduction in the amount of pain after the first PRP application. Based on the degree of osteoarthritis, patients with observed grades I, II, and III also noticed a significant reduction in pain on the VAS scale after the first application of PRP. CONCLUSION. Treatment of knee osteoarthritis by using the intraarticular application of PRP is a successful method as it reduces pain, measured by the VAS scale, in all patients, regardless of their age and degree of osteoarthritis.