Background: Chronic obstructive pulmonary disease (COPD) is characterized by the presence of airflow obstruction caused by emphysema or airway narrowing, or both. Cigarette smoking, which is the major risk factor of COPD, causes the abnormalities by inducing inflammation in the lung parenchyma and peripheral airways. A large number of studies have been done to detect and Quantify pulmonary emphysema using computed tomography (CT). Low attenuation areas (LAA) on CT scans in vivo have been shown to represent macroscopic or microscopic emphysematous changes in the lungs of patients. Although the CT measurement of LAA correlates well with diffusing capacity, the relationship to measurements of airflow obstruction is less significant presumably because airflow obstruction is related to both loss of recoil and inflammatory narrowing of the airways. We hypothesized that the diversity of morphological Changes on HRCT may be associated with the differences in severity of disease and prognosis. To clarify the hypothesis, COPD was classified morphologically using HRCT into the three morphological phenotypes in accordance with the presence or absence of apparent emphysema and bronchial wall thickening, and examined the association of the morphological characteristics on HRCT with severity of disease and prognosis using BODE index.