Idiopathic pulmonary fibrosis (IPF) is relatively common diffuse infiltrative lung disorders and has a progressive course. There are two histologic forms of IPF, UIP  (usual interstitial pneumonia) and DIP (desquamative interstitial pneumonia). The histologic UIP pattern is also one of pulmonary involvement associated with collagen vascular disease. The following computed tomographic findings are observed in patients with UIP: an accumulation of small cystic spaces with thick walls (macroscopic honeycombing), air bronchilograms within areas of intense lung attenuation, rugged pleural surfaces, irregular thickening of pulmonary vessels and interlobular septa, bronchial wall thickening and ground-glass opacity. Upon correlative analysis of CT and pathologic findings, air bronchiolograms in areas of intense lung attenuation corresponded to dilated bronchioles (greater than 1mm in diameter) with fibrosis i.e., microscopic honeycombing. Irregular vessels, interlobular septal thickening and irregular pleural surfaces are attributable to fibrosis in the periphery of the secondary pulmonary lobules. CT features provide significantly higher accuracy in the radiologic diagnosis of UIP. It is reported that, since ground-glass opacity correlated with alveolar septal inflammation, ground-glass opacities may be a potential marker of disease activity in patients with IPF