Until recently, solitary coin lesions of pulmonry disease has been a conspicious problem in radiologic diagnosis. it is now well informed that CT has offered high resolution with its objective CT numbers to provide additional information in terms of anatomic and pathologic changes. Here by the aid of CT, the author has reviewed retrospectively patients with various shape of round masses thus illustrating the advantage of it over conventional X-ray in diagnosis. 1. Total 53 patients, including 34 males and 19 females, aging between 19 to 76 years old with nodule or mass of any size ranging 1 to 13cm in diameter were observed. 2. On plain chest X-ray theywere indentified where 50 patients has single round nodule or mass, only one had two masses which were ecchinococcal cysts, and rest two had invisible lesions, only detected by CT. 3. With philips tomoscan 310, CT scan was taken with 12mm thick slice during quiet respiration. Using the ROI cursor the average CT number of the central area was calculated. 1.0cm in side the outer border of the mass. 4. As a consequence of their pathologic features, they were itemized to 4 group as 36 solid, 9 cystic, 4 consolidative and 4 cavitary lesions. 5. Correct diagnosis of 3 cystic lesions, 4 diffuse calcification, 1 A-V malformation were avalilable by CT densitometry. 6. By the aid of better resolution and additional cross-sectional orientation of CT, 3 extrapulmonary lesions, 3 segmental consolidations, 2 bronchocele, and 2 solitary metastasis, were helpful in diagnosis. 7. Also helpful in determining the extent of intrathoracic extent of bronchogenic carcinoma for the same reason but given clues were not more than the ordinary. 8. However, the limitation of the CT densitometry led to miss diagnosis of 3 examples of cystic vs, solid lesions, and CT density of noncalcified granuloma together with bronchogenic carcinoma, did not have a clear cut separation in between. 9. 18.2% of bronchogenic carcinoma had focal calcification but these types of calcification could not be used as benign indicator. 10. Since there are still debates on CT sensitometry and presence of focal calcification alone is not enough to be used as criteria to rule out malignecy, pathologic diagnosis by ciopsy of the lesion seem very essential in those ambignous cases.