Constrictive bronchiolitis obliterans is an important respiratory illness because of its underlying irreversible fibrotic process, and is defined as concentric fibrosis in the bronchiolar submucosal layer with continual external circular scarring. The fibrotic and destructive nature of this lesion is the defining characteristic. Although patchy, the airway may become slit-like or obliterated from this fibrotic process, resulting in bronchiolitis obliterans. Constrictive bronchiolitis is limited to the bronchioles and does not extend into the alveoli. The clinical features of constrictive bronchiolitis consist of a chest radiograph that is often normal, early inspiratory crackles and irreversible airflow obstruction by pulmonary function testing. Chest CT scans show a mosaic pattern, air trapping by the expiratory film, bronchiolectasis and thickened small airway walls. Although idiopathic constrictive bronchiolitis is rare, the lesion is common among lung-transplant recipients. The lesion also occurs from certain types of toxic fumes, some of the connective tissue diseases, specific types of medications and post respiratory infection. Unusual exposures have also been described as a cause of constrictive bronchiolitis, such as consumption of the leafy vegetable Sauropus androgynus in far eastern Asia and from inhaling diacetyl, the ketone butter flavoring used in microwave popcorn production. Empirical treatment consists of corticosteroid and immunosuppressive agents. Antifibrotic agents may be successful in the future. This is generally a nonsteroid-responsive lesion and for disabling disease, lung transplantation can be a successful option.