Pulmonary vasculitis comprises a heterogeneous group of disorders characterized by an inflammatory process damaging the vessel wall, leading to ischaemia and tissue necrosis. Wegener’s granulomatosis, Churg–Strauss syndrome, and microscopic polyangiitis are primary, small-vessel, necrotizing vasculitides linked by an overlapping clinicopathological picture and are referred to collectively as ANCA-associated systemic vasculitis. The European Vasculitis Study Group proposed a clinical staging system based on disease activity, to guide treatment.