Intraarticular platelet-rich plasma (PRP) injection has emerged as a promising treatment for knee osteoarthritis. Studies to date, including multiple randomized controlled trials, have shown that PRP is a safe and effective treatment option for knee osteoarthritis. Intraarticular PRP is similar in efficacy to hyaluronic acid, and seems to be more effective than hyaluronic acid in younger, active patients with low-grade osteoarthritis. Treatment benefits seem to wane after 6-9 mos. There are numerous PRP treatment variables that may be of importance, and the optimal PRP protocol remains unclear. Future investigations should control and analyze the effects of these variables in PRP treatment. High-quality randomized controlled trials are needed to optimize PRP treatment methods and better define the role of PRP in osteoarthritis management in the knee and, potentially, in other joints.