Emphysema is classified by macroscopic examination of inflated lung sections as proximal acinar, panacinar, distal acinar, and/or paracicatricial. Alveolar fenestrations, the earliest morphologic expression of alveolar wall damage, may be defined with the aid of a dissecting or scanning electron microscope. In bronchial obstructive disease, lesions of both the large and small airways contribute to respiratory impairment. The structural changes of chronic bronchitis are, for practical purposes, always associated with severe emphysematous disease. Thus, it is mandatory for the morphologist who evaluates lung specimens for COPD to pay detailed attention to the acinar pattern of destruction of inflated emphysematous lungs as well as to the gross and microscopic pathology of large and small airways. These structural changes should then be correlated with clinical parameters relative to age, sex, air pollutants, cigarette smoking allergy, and hereditary deficiencies of antiproteolytic enzymes.