There are several forms of emphysema that should be considered as distinct disease entities. No university accepted classification system of these forms exists, but correlations of autopsy findings in 1,823 cases over a 12-year period confirm that the radiographic and pathologic features of the emphysemas are readily understood when centrilobular, panlobular, paracicatricial, and localized types of the disease are recognized. Centrilobular emphysema associated with cigarette smoking is the most common form. Panlobular emphysema is associated with alpha 1-protease inhibitor deficiency and pathologically produces uniform enlargement of all air spaces, with a mild basilar predominance. Paracicatricial emphysema is seen adjacent to areas of parenchymal scarring. Localized emphysema represents focal enlargement or destruction of air spaces with otherwise normal lung. A clear understanding of the computed tomographic appearance of all forms of emphysema is essential for the correct diagnosis of parenchymal lung abnormalities.