91 knees with clinically and radiographically diagnosed knee osteoarthritis were randomized to intraarticular injection of either platelet-rich plasma (PRP), hyaluronic acid (HA), or saline. PRP injections demonstrated significant improvement from baseline in function on the Western Ontario and McMaster Universities Osterioarthritis Index (WOMAC) and the International Knee Documentation Committee (IKDC) scores over the entire 12-month follow-up. HA injections demonstrated improvement from baseline over the first 2 months for WOMAC scores, and over the first month for IKDC scores. Similarly, saline injections only resulted in improvement from baseline over the first month.