In an attempt to differentiate pulmonary cavities of bronchogenic carcinoma from pulmonary tuberculosis we analysed chest roentgenograms in 18 cases of bronchogenic carcinoma and 32 cases of pulmonary tuberculosis in terms of the maximal thickness of the wall eccentricity or concentricity of the cavitation air-fluid level accompanying pulmonary infiltration location and size of the nodules. Cancer cavity showed maximal wall thickness more than 15 mm in 83 % (15/18) eccentric cavitation in 44% (8/18) irregular inner margin in 83% (15/18) Tuberculous cavity showed maximal wall thickness less than 15mm in 91% (29/32) concen-tric cavitation in all cases (32/23) and smooth inner margin in 75% (24/32). Meximal wall thickness more than 15 mm eccentric cavitation and irregular inner margin are suggestive findings of cancer cavity. In contrast maximal wall thickness less than 15mm concentric cavitation and smooth inner margin are suggestive findings of tuberculous cavity. Air-fluid level location and size of the nodule were of some help but not reliable findings.