BACKGROUND: Postprimary pulmonary tuberculosis is located mainly in upper lobes. The tuberculous lesion involving the lower lobes usually arises from the upper lobe cavity through endobronchial spread. When tuberculosis is confined to the lower lung field, it often masquerades as pneumonia, lung cancer, bronchiectasis, or lung ahscess. Thus the correct diagnosis may be sometimes delayed for a long time. METHODS: We carried out, retrospectively, a clinical study on 50 patients confirmed with lower lung field tuberculosis who visited the Department of Pulmonary Medicine at Hanyang University Hospital from January 1992 to December 1994. The following results were obtained. RESULTS: Lower lung field tuberculosis without concomitant upper lobe disease occurred in fifty patients representing 6.9% of the total admission with active pulmonary tuberculosis over a period of 3 years. It occurred most frequently in the third decade but age distribution was relatively even. The mean age was 43 years old. Female was more frequently affected than male (male to female ratio 1:1.9). The most common symptom was cough(68%), followed by sputum(52%), fever(38%), and chest discomfort(30%). On chest X-ray of the S0patients, consolidation was the most common finding in 52%, followed by solitary nodule(22%), collapse(16%), cavitary lesion(l0%), in decreasing order. The disease confined to the right side in 25 cases, left side 20 cases, and both sides 5 cases. Endobronchial tuberculosis (1) Endobronchial involvement was proved by bronchoscopic examination in 20 of S0patients. (2) Mean age was 44years old and female was more affected than man (male to female ratio 1 : 3). Sputum AFB stain and Mycobacterium tuberculosis culture were positive only in 50% of cases unlikely upper lobe tuberculosis, additional diagnostic methods were needed. In our study, bronchoscopic examination and percutaneous fine needle aspiration biopsy increased diagnostic yield by 18% and 32%, respectively. The most common associated condition was diabetes mellitus(18%) and others were anemia, anorexia nervosa, stomach cancer, and systemic steroid usage. CONCLUSION: When we find a lower lung field lesion, we should suspect tuberculosis if the patient has diabetes mellitus, anemia, systemic steroid usage, malignancy or other immune suppressed states. Because diagnostic yield of sputum AFB smear