Osteoarthritis is the most prevalent joint disease and a frequent cause of joint pain, functional loss, and disability. Osteoarthritis often becomes chronic, and conventional treatments have demonstrated only modest clinical benefits, without lesion reversal. Cell-based therapies have shown encouraging results in both animal studies and a few human case reports. We have recently published the results of a pilot clinical trial designed to assess the feasibility and safety of osteoarthritis treatment with bone marrow–derived mesenchymal stromal cells (MSCs) in 12 patients with chronic knee pain unresponsive to conservative treatments and radiologic evidence of osteoarthritis. The patients were treated with autologous expanded bone marrow MSCs by intra-articular injection (40×106 cells), and clinical outcomes, including evaluations of pain, disability, and quality of life, were followed up for 1 year. Articular cartilage quality was assessed by quantitative magnetic resonance imaging (MRI) T2 mapping.