Emphysema is defined as a condition of the lung characterized by abnormal, permanent enlargement of airspaces distal to the terminal bronchiole accompanied by destruction of the alveolar walls and without obvious fibrosis. It is a very common disease with high morbidity and mortality. Histopathologically, there are two types of emphysema: panlobular emphysema, typically occurring in alpha1-antitrypsin deficiency, and centrilobular emphysema, which is strongly associated with cigarette smoking. Computed tomography (CT) allows detection of emphysema with higher sensitivity than conventional chest radiography and pulmonary function tests. CT also allows quantification of emphysema and depicts associated changes and complications. The differential diagnosis of emphysema, which is characterized by the absence of clearly definable walls on CT, includes cystic lung disease, bullae, lung laceration, Langerhans cell histiocytosis, and lymphangioleiomyomatosis -which are all characterized by visible walls on CT.