The detection of cavity in pulmonary tuberculosis has impotant roles in its diagnosis, therapy planning andfollow-up of healing process, and also means at least moderate advanced tuberculosis. The plain chest film hassome limitation of detection of cavity in pulmonary tuberculosis owing to several factors. CT is superior to plainchest film and conventional tomography, in detection of cavitary lesion. Authors retrospectively analized CTfindings of 20 cases of minimal pulmonary tuberculosis, of which the plain chest films showed no cavitary lesionfrom Sept. 1986 to July 1988 in Pusan National University Hospital. All cases were proven by culture of AFB testof 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 onthe plain chest films, but all cases showed variable sized cavities on CT. 3. The size of cavities ranged from 4mm to 30mm, averaged as 9.9mm, the thickness of cavitary wall from 3mm to 8mm, averaged as 5.8mm 4. It is concludedthat cavitary lesions which are not visualized on the plain chest films can be demonstrated by CT scan in minimalpulmonary tuberculosis.