PURPOSE: The aim of our study was to identify the CT features helpful in the differential diagnosis of Iobar consolidation. MATERIALS AND METHODS: We evaluated the CT findings in 52 consecutive patients with Iobar consolidation which were proved to be pulmonary tuberculosis(n=24), malignant obstructive pneumonitis due to bronchogenic carcinoma(n=21), and lung abscess(n=7). We retrospectively reviewed CT scans with respect to 1) number of cavities or low attenuation area suggesting necrosis(we described these as cavity), 2) the contour of cavity, 3) enhancement of the cavity wall, 4) enhancement of pleura, 5) small nodules adjacent to the consolidation, 6) similar lesion in other location in lung, 7) air-bronchogram 8) mediastinal lymph node enlargement, and 9) extrapleural change. RESULTS: The helpful CT fingings in the patients with pulmonary tuberculosis were multiple cavities(more than three;79.2%), small nodules adjacent to the Iobar consolidation(75.0%), similar lesion in another lobe or lung(91.7%), air-bronchogram(91.7%), and mediastinal lymph node enlargement(58.3%). Although extrapleural change had low sensitivity it was highly specific for pulmonary tuberculosis(sensitivity, 43.5%;specificity, 91. 7%). Multiple cavities(61.9%) and mediastinal lymph node enlargement(52.4%) were common findings of malignant obstructive pneumonitis. In the patients with lung abscess, the common findings were small number of cavities(one or two, 85.7%) and air-bronchogram(85.7%). However, other findings of pulmonary tuberculosis were rarely seen in the patients with malignant obstructive pneumonitis or lung abscess. CONCLUSION: The CT findings of Iobar consolidation may be used as useful adjuncts in the differential diagnosis of Iobar consolidation.