Adult-onset Still disease (AOSD) is an inflammatory condition of unknown etiology that responds to glucocorticosteroids and disease-modifying antirheumatic drugs, particularly methotrexate. However, disease refractory to conventional treatment has led to the reported use of biologic therapy including tumor necrosis factor α inhibitors (infliximab, etanercept, and adalimumab), anakinra, rituximab, and tocilizumab. We report the successful use of abatacept in the treatment of a patient with AOSD manifested by polyarthritis, rash, fevers, elevated liver function tests, and ferritin levels refractory to treatment with methotrexate and hydroxychloroquine. Remission has been maintained for 35 months with the addition of abatacept administered once monthly. There is evidence that T-cell activity plays an important role in the autoimmune activity of AOSD, and modulation of CD28 costimulation of T cells by abatacept has specific immunosuppressive actions that make it an appealing alternative therapeutic option for refractory AOSD.