A 55-year-old man, with no previous history, presented with extreme fatigue and fever and was admitted to hospital. He had progressive renal dysfunction and his serum anti-neutrophil cytoplasmic antibodies (ANCA) were markedly elevated. Renal histology was consistent with ANCA-associated vasculitis. The patient was successfully treated with cyclophosphamide and prednisolone. The classification and management of the ANCA-associated vasculitides are described. The classification was guided by the clinical presentation, serology and results of tissue biopsies. The ANCA inflammation had affected the middle sized and small vessels of especially the upper and lower airways, and the kidneys. The antibodies were directed at proteinase-3 (PR3) or myeloperoxidase (MPO). PR3-ANCA is predominantly found in Wegener's granulomatosis, while MPO-ANCA is related to microscopic polyangiitis. Tissue studies showed granulomatous inflammation of the airways which is typical of Wegener's disease. This type of inflammation is absent in microscopic polyangiitis. The initial treatment schedule consists of prednisone 1 mg/kg daily and oral cyclophosphamide 2 mg/kg daily. In the remission phase, the cyclophosphamide is replaced by azathioprine. It is not yet known how long maintenance treatment should be continued and which parameters have prognostic value.