Bronchiolitis obliterans (BO) is a rare form of chronic obstructive lung disease that follows an insult to the lower respiratory tract.¹ It is characterised by inflammation and fibrosis of the terminal and respiratory bronchioles that lead to narrowing and/or complete obliteration of the airway lumen. Pathologically, two forms of BO are recognised, and these may be part of a continuum. Proliferative bronchiolitis is characterised by intraluminal exudates, whereas constrictive bronchiolitis is characterised by alterations in the walls of the bronchioles ranging from inflammation to fibrosis and, ultimately, to complete obliteration of the lumen.² The histological findings of constrictive bronchiolitis are a common end point for many disorders that are associated with airway epithelial injury including allograft recipients (lung, heart-lung, and bone marrow), previous lower respiratory tract infection (adenovirus,^3–,⁶ influenza,⁷ parainfluenza, measles, respiratory syncytial virus,⁸ or Mycoplamsa pneumoniae^9–,¹¹), collagen vascular disease (especially rheumatoid arthritis and Sjogren’s syndrome), toxic fume inhalation, chronic hypersensitivity pneumonitis, drugs (such as penicillamine or cocaine), and Stevens-Johnson …