Microscopic polyangiitis is a systemic necrotizing vasculitis affecting small vessels, without granulomata. Patients present with rapidly progressive glomerulonephritis, often associated with cutaneous, musculoskeletal, neurological or gastrointestinal involvement. Antineutrophilcytoplasmic antibodies are frequently found, most often with a perinuclear pattern and a antimyeloperoxidase specificity. Diagnosis is based on the evidence of a necrotizing glomerulonephritis, or histological vasculitis, in the absence of extravascular granulomata or sign of macroscopic polyarteritis nodosa. Corticosteroids and immunosuppressive drugs have improved the prognosis, but relapses are frequent.