93 patients with early-stage osteoarthritis (OA) of the knee were randomized to receive either a single cycle of platelet-rich plasma (PRP) treatment consisting of 3 injections, or to receive the same treatment plus an additional second cycle, repeated 1 year later. Patients were followed-up for a minimum of 2 years after initiation of treatment. The purpose of the study was to determine if annual repetition of the treatment resulted in pain reduction, improvement in quality of life or ability to participate in activities compared to a single course of injections. Results indicated a significant benefit to pain, activity level, and quality of life in the repeat injection group 18 months into treatment, although the differences were no longer significant at 24 months.