Pulmonary vasculitis is characterised by inflammation of vascular walls with their destruction. The vasculitis usually reflects the pulmonary vascular component of a systemic vasculitis. The aetiolopathogenesis of many vasculitic disorders is unknown, and it is likely that genetic-environmental interaction is important to the causation. This chapter adopts a syndrome-based approach to the diagnosis of vasculitis. It lists the issues of relevance during the initial assessment of the patient with a probable pulmonary vasculitis and the conditions against the background of which pulmonary vasculitis should be suspected. It incorporates a cohesive strategy for the preliminary diagnosis of vasculitis based on the organ systems involved. It discusses the conditions to consider in the setting of anti-nuclear nuclear cytoplasmic antibody (ANCA)-positivity and attempts to distinguish between these conditions based on a combination of clinical manifestations and ANCA-testing. It also discusses context-based testing for ANCA in the light of the possibility of false-positive and false-negative results. Finally, it examines the role of histopathological sampling in the diagnosis of the ANCA-positive vasculitides, highlighting those conditions that present with specific pathological patterns.