Bronchiolitis is an inflammatory or fibrosing process that primarily affects the small airways, often sparing a considerable portion of the interstitium. Although acute bronchiolitis, mainly caused by viruses, is the most frequently recognized affliction of the bronchioles in the pediatric age group, diseases primarily located in the small, peripheral airways of the lung are reported in various clinical settings. Bronchiolar injury includes infection, collagen-vascular diseases, reaction to drugs, exposure to toxic fumes, and may follow organ or bone marrow transplantation. In addition, bronchiolar involvement may be seen in conditions that are more suggestive of an interstitial lung disease and it frequently accompanies diseases of the large airways. The purpose of this review is to provide a description of the spectrum of childhood bronchiolar disorders and the different clinical settings in which they occur. A summary of both the anatomic and histologic characteristics of small airways is given. A comprehensive description of the clinical presentation of bronchiolitis, functional impairment, and radiologic features is reported, with special emphasis on the role of high resolution computed tomography in the diagnosis of pediatric diffuse lung diseases and to the therapeutic options.