Respiratory involvement in patients with inflammatory bowel disease (IBD) has been reported mainly since 1976. This form of involvement should clearly be separated from interstitial lung disease due to sulfasalazine or mesalamine, although the distinction may be difficult in some cases. We report the data of an ongoing Registry containing 33 cases (23 cases receiving no drug therapy) with ulcerative colitis or, less often, Crohn's disease, who developed varied bronchopulmonary problems. In several cases, the exact diagnosis and the relation of the bronchopulmonary disease to IBD had not been established for many years, thus delaying effective treatment with steroids. In most cases (28/33), respiratory involvement followed the onset of IBD (8 of these 28 cases were postcolectomy), and in the remainder, respiratory manifestations predated the IBD. Patterns of involvement included: 1) Airway inflammation, in the form of subglottic stenosis, chronic bronchitis, severe chronic bronchial suppuration, bronchiectasis, and chronic bronchiolitis. In cases with large airway involvement, endoscopy showed exuberant inflammatory tissue in the airways and narrowing of tracheal and/or bronchial lumen. Histologically, airways were heavily infiltrated by a dense aggregate of inflammatory cells, and there were mucosal ulcerations. 2) Varied patterns of interstitial lung disease, mainly bronchiolitis obliterans with organizing pneumonia, and pulmonary infiltrates and eosinophilia. (3) Miscellaneous other forms of involvement including striking neutrophilic necrotic parenchymal nodules (corresponding histologically to sterile aggregates of neutrophils), and serositis. Steroids were very effective in the majority of cases. Inhaled steroids were of durable benefit in patients with chronic bronchitis, but less often so in those with chronic bronchial suppuration, bronchiectasis, or chronic bronchiolitis. Steroids administered orally led to marked improvement in patients with interstitial lung disease and necrotic nodules, but lacked effectiveness in several patients with severe airway inflammation or chronic bronchiolitis. Intravenous steroids were required in the initial management of life-threatening complications such as asphyxiating subglottic stenosis or extensive interstitial lung disease. Bronchial lavages with methylprednisolone were effective in some patients with severe airway inflammation. Patients with IBD can develop varied inflammatory complications in the lung, and a sizable fraction of these complications is steroid-sensitive.