Differential diagnosis of cavitary lung lesions is frequently problematic. We studied 35 patients with cavitary lung lesions, consisting of lung cancer (17 patients). Pulmonary tuberculosis(11 patients), and lung abscess (7 patients). We analysed CT scans in terms of irregularities of the cavity wall, maximum wall thickness, the presence of air-fluid level, location of the cavity within the mass, number of cavities within the mass, size of the cavity and the presence of calcification within the mass. Cancer cavity showed irregular inner (100%) and outer margins(100%), and thick wall (mean, 1.94cm), eccentrical location(94%) and multiplicity within a mass(38%). Tuberculous cavity showed smooth inner (56%) and irregular outer margins(75%), thin wall (mean 0.96cm), central location (62%), and multiplicity in one patient (36%). Abscess cavity showed irregular inner (57%) and outer margins(91%), relatively thin wall (mean 1.0cm), central location (57%), and air-fluid level (86%). CT scan could differentiate malignant lesions from benign condition such as tuberculosis and lung abscess by observing characteristics of the cavities.