We describe 6 patients with chronic interstitial lung disease in whom open lung biopsies showed respiratory bronchiolitis. The patients ranged from 28 to 46 yr of age (mean, 36 yr) and included 5 men and 1 woman. All were heavy cigarette smokers. Five had respiratory symptoms, most commonly cough and dyspnea. Diffuse interstitial infiltrates were seen on chest radiographs in 5 and bibasilar atelectasis in 1. Pulmonary function tests showed mild to moderate restriction in 4 and decreased diffusing capacity in 4. The initial pathologic interpretation in 3 patients suggested a variant of idiopathic pulmonary fibrosis, and these patients received corticosteroids because of this diagnosis. All patients have remained stable or improved after a mean follow-up of 3.2 yr. Respiratory bronchiolitis should be recognized as an uncommon cause of chronic interstitial lung disease. It must be separated from the other diseases in this category because of marked differences in treatment and prognosis.