A rare, fulminant small vessel vasculitis that affects the capillary beds of the kidneys and lungs and characterized by the presence of anti-glomerular basement membrane (GBM) and, in its full-blown form, anti-alveolar basement membrane (ABM) antibodies. Consequently, it may manifest as a rapidly progressive, isolated glomerulonephritis (anti-GBM nephritis) or as a pulmonary-renal syndrome with severe lung hemorrhage.