Patients referred for assessment of severe chronic airflow obstruction over a three-year period were reviewed, and when all smokers and ex-smokers, those with asthma, chronic bronchitis, emphysema, and other specific pulmonary diagnoses were excluded 10 patients remained. Their clinical, lung function, and bronchographic features were consistent with obliterative bronchiolitis. Nine were women, five had rheumatoid arthritis, and five had survived for more than 10 years after first symptoms. Obliterative bronchiolitis has not previously been considered as a cause of chronic airflow obstruction but the distinctive features suggest that it is a true disease entity.