The aim of this case report is to evaluate the efficacy of mesenchymal stem cell (MSC) therapy in the treatment of small joint osteoarthritis (OA). Acromio-clavicular (AC) joint OA is an under-diagnosed and yet frequent source of shoulder pain. MSCs have shown evidence of benefit in the treatment of knee OA. This is the first report to describe the use of MSC therapy in OA of the upper limb. A 43-year-old patient presents with painful AC joint OA and undergoes MSC therapy. The patient reported pain and functional improvement as assessed by the Disability of Arm, Shoulder and Hand Score and Numeric Pain Rating Scale. Imaging at 12 months showed structural improvement with reduction in subchondral oedema, synovitis and subchondral cysts. This case is the first to show the benefit of MSC therapy in the treatment of small joint arthropathy and also of the upper limb.