413 patients with knee osteoarthritis and low vitamin D levels were randomized to a monthly treatment of either oral vitamin D3 or an identical placebo for 24 months. The purpose of this study was to determine whether or not vitamin D supplements are beneficial in mitigating knee pain and improving knee cartilage volume, when compared with placebo up to 2 years. Findings indicated no significant difference in changes in tibial cartilage volume, WOMAC knee pain, tibiofemoral cartilage defects, or tibiofemoral bone marrow lesions between treatment groups.