PURPOSE: To determine whether tuberculous pneumonia can be distinguished from community-acquired pneumonia on the basis of chest radiographic findings only and the diagnostic utility of differences in serum CA-125 levels. MATERIALS AND METHODS: Forty-five patients with a high fever (>38 'C) in whom chest radiography revealed lobar consolidation were retrospectively studied. In 27 cases, the presence of acid-fast bacilli in sputum (n=21), the isolation of Mycobacterium tuberculosis from bronchoscopic biopsy tissue and sputum cultures (n=16), and improvement in the findings of serial radiography and in clinical symptoms during antituberculous therapy (n=1) let to a diagnosis of tuberculous pneumonia. A diagnosis of community-acquired pneumonia (n=18) was based on improvement in the serial radiographic findings obtained during antibacterial therapy (n=16), and the isolation of bacteria from sputum and pleural fluid culture (n=2). On the basis of independently analysed findings, radiologist determined the presence or absence of nodular density, cavitary lesions and loss of lung volume, while two radiologists differentiated between tuberculous pneumonia and community-acquired pneumonia. RESULT: Initial chest radiographs of tuberculous pneumonia revealed nodular density in 89% of cases, cavitary lesions in 29%, and loss of lung volume nodular density was in 26%, while those of community-acquired pneumonia demonstrated nodular density in only 22%, cavitary lesions in 6%, and loss of lung volume in none was a significant statistical difference in nodular density, cavitary lesions and loss of lung voume (p<0.005). The average serum CA-125 level in tuberculous pneumonia was 306.5 (range, 21.3 -1078) U/ml, whereas the average level in community-acquired pneumonia was 38.0 (range, 11.3 -114.8) U/ml (p<0.005). CONCLUSION: Initial chest radiography can differentiate between tuberculous and community-acquired pneumonia on the basis of nodular density, cavitary lesions and loss of lung volume and differences in CA-125 levels also provide a useful means of differentiating between these pneumonias.