Objectives This study aimed to analyze the efficacy of platelet-rich plasma obtained from the peripheral, autologous blood of the patients in pain complaints reduction and functional improvement of knee osteoarthritis compared with the standard treatment with injectable corticosteroid, such as triamcinolone. Methods The patients were followed-up clinically at the preinfiltrative visit, with quantitative evaluation using the Knee Society Score (KSS), the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, and the Kellgren and Lawrence scales. In addition, they were reevaluated with the same scales after 1 month and 6 months of intervention with 2.5 mL of triamcinolone acetate or 5 mL of platelet-rich plasma. The study was performed on 50 patients with knee osteoarthritis treated at the Medical Specialty Center and randomly divided into equivalent samples for each therapy. Results The present study verified the reduction of pain scores, such as the WOMAC score, and elevations of functional scales, such as the KSS, evidenced in 180 days when using platelet-rich plasma, a therapy that uses the autologous blood of the patient and has fewer side effects. Conclusion Although both platelet-rich plasma and corticosteroid therapies have been shown to be effective in the reduction pain complaints and functional recovery, there was a statistically significant difference between them at 180 days. According to the results obtained, platelet-rich plasma presented longer-lasting effects within 180 days in the treatment of knee osteoarthritis.