The detection of cavity in pulmonary tuverculosis has important roles in its diagnosis therapy planning and follow-up of healing process and also means at least moderate advanced tuberculosis. the plain chest film has some limitation of detection of cavity in pulmonary tuberculosis owing to several factors, CT is superior to plain chest tilm and conventional tomography in detection of cavitary lesion. Authors retrospectively analized CT findings of 20 cases of minimal pulmonary tuberculosis of which the plain chest films showed no cavitary lestion from Sept. 1986 to July 1988 in Pusan national University Hospital. All cases were proven by culture of AFB test of sputum and clinical evidence. The results were as follows; 1. sex distribution showed 10 cases (50%) in male 10 cases (50%) in female and the highest incidence in the second decade(40%) 2. All 20 cases showed no cavity on the plain chest films but all cases showed variable sized cavities on CT. 3. The size of cavities ranged from 4mm t 30 mm averaged as 9,9mm the thickness of cavitary wall from 3mm to 8mm averaged as 5,8mm 4, It is concluded that cavitary lesions which are not visualized on the plain chest films can be demonstrated by CT scan in minimal pulmonary tuberculosis.