Bronchiolar diseases pose a significant challenge to the clinician confronted with the evaluation and management of the affected patient. A variety of infectious and non-infectious diseases may affect the bronchioles causing either reversible or fixed bronchiolar obstruction. High-resolution CT (HRCT) is currently the best imaging modality for evaluation of small-airway disease. In fact, a wide spectrum of abnormalities are identified at HRCT in patients with bronchiolar diseases. These abnormalities are shown on HRCT in the presence of a normal or unclear chest radiograph. Additionally, HRCT performed at suspended full expiration may demonstrate the physiologic consequences of bronchiolar disease, e. g., air trapping. The differential diagnosis of pulmonary manifestations of bronchiolar diseases at HRCT is based on the different patterns of abnormality. Familiarity with the presentation of different bronchiolar inflammatory processes aid the radiologist in narrowing the differential diagnosis or even in suggesting a specific diagnosis. This article reviews the HRCT findings of various bronchiolar inflammatory diseases outlining their pathologic features. Knowledge of the underlying gross and microscopic pathologic features leads to a better understanding of their CT appearances.