PURPOSE: To analyse and compare high-resolution CT findings of pulmonary tuberculosis with consolidation and mycoplasma pneumonia. MATERIALS AND METHODS: Twenty patients with pulmonary tuberculosis [confirmed by sputum culture (n=9) and bronchoscopic biopsy (n=11)] and airspace consolidation on high-resolution CT and 17 patientswith mycoplasma pneumonia, confirmed by serologic test, were included in this study. High-resolution CT findings were analyzed in terms of ground-glass opacities, distribution of consolidation, type of nodules, cavities, interlobular septal thickening, bronchial dilatations, bronchial wall thickening and pleural effusion. RESULTS: In patients with tuberculsis, average age was 33.5 years (range, 20-67) ; in those with mycoplasma pneumonia it was 32.5 years (range, 17-74). Segmental and subsegmental distributions were most common in both diseases ; the preferred site of consolidation was different, however ; for tuberculosis it was the upper lobes (13 cases, 65% ; bilateral involvement, 7 cases) ; for mycoplasma pneumonia it was the lower lobes (11 cases, 64.7%). Non-segmental (diffuse and random) distribution of ground-glass opacities were seen in two patients(11.8%) with mycoplasma pneumonia. Centrilobular nodules, branching linear opacities and alveolar nodules were not different in both diseases, but there were nodules above 10mm in 14 cases of tuberculosis and in only one case of mycoplasma pneumonia. Tree-in-bud appearances were seen in five cases of tuberculosis. Cavities without air-fluid level were noted in ten cases of tuberculosis. Other interlobular septal thickening, bronchial wall thickening, bronchial dilatation and pleural effusion were not different in both diseases. CONCLUSION: There was considerable overlap between high resolution CT findings of tuberculosis with airspace consolidation and those of mycoplasma pneumonia. The location of consolidation, type of nodules, and the presence of tree-in-bud appearance and cavities help in the differentiation of the two diseases, however.