Wall thickness and inner wall nodularity are two major criteria in the differential diagnosis of benign and malignant cavitating pulmonary nodule by using conventinal radiographs. It is assumed that post-contrast enhanced CT scan differentiated necrotic and viable portion of the cavity wall by difference in CT density. To evaluate the difference in terms of diagnostic accuracy between the two methods ; measuring summed up thickness of both lower (necrotic) and higher (viable) density portion and measuring only higher density portion, 37 cavitary lung masses(18 malignant, 19 benign) from 32 patients were studied retrospectively. CT measurements were compared with that of plain radiographs. The mean thickness of the thickest part of the wall were 20$pm$13mm and 30$pm$17mm in benign and malignant cavity(p>0.05), respectively, when both lower and higher density were measured. However, when measured only higher density portion, the means were 5$pm$3mm in benign and 15$pm$9mm in malignant l sions, of which difference was statistically significant (p<0.01). The thickest part of the higher density portion was less than 5mm in all 14 benign lesions, while seven of eight (87.5%) malignant lesions had 16mm or greater. The inner wall of the cavity was smooth in 84.2% and 6% of the benign and malignant lesions, respectively. In conclusion, our data suggests that assessing the wall thickness and inner wall nodularity by measuring higher (enhancing) density portion of the cavitary mass is superior to the methods that measures the whole wall thickness.