The primary systemic vasculitides are a group of diseases characterized by an inflammatory process of the vessel walls and classified according to the smallest vessels involved. Small vessel vasculitides comprise the largest subgroup divided into diseases with a pauci-immune vasculitis and ANCA and diseases with deposition of immunoglobulin without ANCA. ANCA-associated systemic vasculitides include Wegener's granulomatosis, microscopic polyangiitis comprising renal-limited vasculitis and Churg-Strauss syndrome. Diagnosis is based on clinical manifestation, ANCA-testing and histology. Beside the role of ANCA as a diagnostic marker many studies and animal models have focused on the pathogenic role. The treatment of ANCA-associated vasculitis has changed from a standardized "Fauci-protocol" to an individualized less toxic strategy taking into consideration disease severity) organ manifestation, age of the patient and individual risk factors (e.g. increased bone marrow toxicity in patients with renal insufficiency). For remission induction patients are sub-grouped according to limited or generalized disease with moderate or severe renal involvement. Thus cyclophosphamide is only used in patients with generalized disease or - regarding Churg-Strauss-syndrome - patients with risk factors. For maintenance of remission azathioprine should be used in most of the patients.