Diffuse panbronchiolitis (DPB), an important cause of progressive obstructive lung disease in the Far East, represents a distinctive sinobronchial syndrome with typical radiologic and histologic features. We have identified DPB in five citizens of the United States, three with histologic confirmation, who have never traveled to the Far East. There were four men and one woman, whose ages ranged from 46 to 75 yr at the time of diagnosis. All had a prior history of chronic sinusitis and presented with cough, dyspnea, and sputum production. Three were never smokers and two were current smokers. Pulmonary function testing revealed severe airflow limitation (the FEV1 ranging from 22% to 56% of predicted), and overdistention. All patients had high-resolution computed tomographic (HRCT) scans indicating centrilobular nodules with adjoining thickened and dilated bronchioles. In the three patients in whom open lung biopsy was performed, there was bronchiolocentric infiltration of lymphocytes, plasma cells, and foamy macrophages. Three patients remain alive and are being treated with chronic macrolide therapy. The clinical, radiographic, and histologic features of these patients closely resemble those described in Japanese patients. DPB must be considered in the differential diagnosis of sinopulmonary syndromes, bronchiolitis, and cryptic cases of obstructive lung disease among United States citizens, since therapy now offers an improved prognosis.