PURPOSE: To evaluate the role of HRCT in the differentiation of pulmonary tuberculosis and lung cancer, where the manifestation of disease is a solitary pulmonary nodule(SPN). MATERIAL AND METHODS : Forty eight SPNs including 29 cancers proven by surgery(n=10), by bronchoscopic biopsy(n=7) and by fine needle aspirationbiopsy(n=12), and 19 tuberculous nodules proven by surgery(n=4), by bronchoscopic biopsy(n=4), by fine needle aspiration biopsy(n=5), by a positive result in AFB culture without evidence of malignant cells(n=3), and by adecrease in size on serial plain chests despite negative AFB culture(n=3) were included. Scanning parameters forHRCT were 140KVp, 170mA, 1.5mm collimation, 3 sec scanning time, and a high spatial frequency algorithm was used. RESULTS: With regard to the marginal features of nodules, the findings mor commonly observed in malignant nodules were greater average length of the longest spicule(5.35 ±3.19mm versus 2.75 ±1.56mm), and more commonspiculated nodules greater than 3cm in diameter, 16(55%) versus 2(10.5%)(P<0.05). Regarding the internal characteristics of nodules and perinodular parenchymal changes, the findings more commonly observed in cases of cancer were air-bronchograms within nodules(14;48.3%) and interlobar fissure puckering(6;20.7%), whereas intuberculosis cases the most common findings were low density of nodule(16;84.2%), cavitation(12;63.1%), and perinodular focal lung hypodensity(5;26.3%),(p<0.05). No statstically significant difference was observed between the incidence of satellite lesions of tuberculous(73.7%) and of malignant nodules(34.5%). However, perilobular nodules or bronchovascular bundle thickenings were more commonly observed in the satellite lesions of malignant nodules(9;90%), whereas centrilobular nodules or lobular consolidation were more commonly observed in those of tuberculous nodules(12;85.7%),(p<0.05). CONCLUSION: HRCT provides detailed information concerning perinodularparenchymal changes and characteristics of satellite nodules as well as marginal features and internal characteristics of SPNs which may play a significant role in differentiating pulmonary tuberculosis from malignant nodules.