The idiopathic (BOOP) and secondary forms of proliferative bronchiolitis have similar radiographic appearances. Both are characterized radiographically by patchy airspace disease, which often is peripheral. The radiographic presentation of BOOP may have prognostic significance. In primary or secondary constrictive bronchiolitis, the chest radiograph often is nonspecific, but the CT appearance of patchy, lobular areas of hyperlucency, with or without bronchiectasis, may be diagnostic. Respiratory bronchiolitis usually can be distinguished from IPF on the chest radiograph, and the diagnosis may be suggested on HRCT by the presence of hazy increase in lung density or fine centrilobular nodules.