PURPOSE: We evaluated internal and marginal features of solitary pulmonary nodules on CT to differentiate between benign and malignant pulmonary nodules. Materials and Uethods:CT findings of 43 cases with solitary pulmonary nodule were reviewed, restrospectively. Independent T-test between benign and malignant nodules was used. RESULTS: Twenty-one cases were proved as benign nodules and 22 cases as malignant. CT air bronchogram was observed more frequently in the malignant lesions(36.4%) than in the benign ones (p=0.01). ,Air bubble shadow was observed in 5 cases of benign nodule, whereas none of the malignant lesions revealed it. Internal homogeneity or central low density was not different between the two groups. Cavitation was observed in 3 cases of tuberculoma and in 1 case of adenocarcinoma. Calcification was observed in 7 cases of benign and in 2 cases of malignant lesions. Differences in these two features were not statistically significant Mean size of malignant nodules was 3.23cm, and was larger than 2.16cm of benign nodules (p=0.002). Margin of benign nodules was more smooth (42.9%) than that of malignant nodules (p=0.01), and malignant nodules showed more Iobulated contour (90.9%) than benign nodules (42.9%) (p=0.00). The incidence of spiculation was not significantly different (benign 85.7% vs malignant 86.4%). Statistically, pleural tail and satellite lesions were not significantly different between two groups. CONCLUSION: Lobulated margin and CT air bronchogram are the most suggestive findings of malignant pulmonary noule on chest CT.