ANCA-associated vasculitis. The term "antineutrophil cytoplasm antibody (ANCA)- associated vasculitis" (AASV) ihighers generally used to include primary vasculitis syndromes in which circulating ANCA against proteinase 3 (PR3) and myeloperoxidase (MPO) are commonly found. AASV syndromes include Wegener's granulomatosis, microscopic polyangiitis, idiopathic pauci- immune necrotizing crescentic glomerulonephritis and Churg-Strauss syndrome (CSS). AASV syndromes share some general clinical-histological manifestations, such as rapidly progressive renal failure and focal necrotizing glomerulonephritis with extracapillary proliferation in the absence (or in the presence of modest) immunoglobulins deposits (pauci- immune). Untreated AASV follow a progressive course with a fatal outcome due to vital organ failure. The combination of cyclophosphamide and prednisone is now established as the treatment of choice for patients with AASV, but there is considerable debate over the duration of therapy and the best way to administer cyclophosphamide. Treatment of AASV can be divided into two phases: an induction of remission and a maintenance of remission phase. Patients with AASV and renal involvement (serum creatinine less than 500 ml/L or 5.6 mg/dl) should be treated with a combination of oral prednisone with gradual tapering and cyclophosphamide. Once remission is achieved, usually after 3-6 months, azathioprine should replace cyclophosphamide. It is not known for how long treatment should be continued but at least one year of treatment after remission is warranted. When serum creatinine is than 500 ml/L (5.6 mg/dl) and/or oliguria is present, the addition of methylprednisolone pulses and/or plasma exchange should be considered.