The results of an open-label prospective trial with 20 patients indicate that abatacept could be an effective therapy for long-standing, non-severe relapsing granulomatosis with polyangiitis (formerly Wegener's granulomatosis). Following treatment with abatacept 10 mg/kg by intravenous infusion on days 1, 15, 29 and every 4 weeks thereafter, 18 (90%) showed improvement in disease activity and 16 (80%) achieved remission, as measured by use of the Birmingham Vasculitis Activity Score for Wegener's Granulomatosis. The median length of time on the study was 12.3 months (range 2–35 months). Of note, any therapy with methotrexate, azathioprine or mycophenolate mofetil was continued, whereas glucocorticoid therapy was permitted only for the first 2 months (11 of 15 patients on prednisone successfully tapered to 0 mg).