The identification of antineutrophil cytoplasmic antibodies (ANCA) proved a major breakthrough in the classification, diagnosis, monitoring, and understanding of vasculitides. Vasculitides associated with ANCA selectively affect the small vessels; they include Wegener granulomatosis, microscopic polyangiitis, and Churg-Strauss syndrome. Evidence supporting a direct pathogenic role for ANCA has accumulated over the years. The clinical, laboratory, and histological findings vary across diseases; they are discussed here based on a review of published data from over 1600 patients. The course and prognosis also vary according to the disease. New treatment strategies tailored to the type and extent of the vascular disease have improved survival and treatment safety. Induction therapy, which should be given on an emergency basis in a specialized unit, consists of glucocorticoid therapy and cyclophosphamide in Wegener granulomatosis; microscopic polyangiitis and Churg-Strauss syndrome, without poor prognostic factors, can be managed with glucocorticoid therapy alone as the first-line treatment. A full recovery or complete remission is now achieved in over 80% of patients. Maintenance therapy is mandatory to reduce the relapse rate, which varies across diseases. Among patients with Wegener granulomatosis, up to 50% relapse within the first 5 years. Azathioprine is the main maintenance drug, although methotrexate, mycophenolate mofetil, or leflunomide may be used as second-line drugs. Biotherapies such as rituximab and TNFalpha antagonists are currently under evaluation as promising rescue agents for patients with refractory disease.