Wall thickness and inner wall nodularity are two major criteria in the differential diagnosis of benign andmalignant cavitating pulmonary nodule by using conventinal radiographys. It is assumed that post-contrast enhancedCT scan differentiate necrotic and viable portion of the cavity wall by difference in CT density. To evaluate thedifference 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 lungmasses(18 malignant, 19 benign) from 32 patients were sudied retrospectively. CT measurements were compared withthat of plain radiographs. The mean thickness of the thickest part of the wall were 20±13mm and 30±17mm inbenign and malignant cavity(p<0.05), respectively, when both lower and higher density were measured. However, whenmeasured only higher density portion, the means were 5±3mm in benign and 15±9mm in mallignant lesions, of whichdifference was statistically significant (p<0.01). The thickest part of the higher density portion was less than5mm in all 14 benign lesions, while seven of eight(87.5%) malignant lesions had 16mm or greater. The inner wall ofthe cavity was smooth in 84.2% and 6% of the benign and malignant lesions. respectively. In conclusion, our datasuggests that assessing the wall thickness and inner wall nodularity methods that measures the whole wallthickness.