PURPOSE: To describe radiologic differences between tuberculous pleural effusion and empyema on the basis of computed tomography(CT). MATERIALS AND METHODS: We reviewed retrosepectively CT findings of 50 patients with pathologically and grossly proved empyema. Twenty-two patients had empyema, and 28 patients had tuberculous pleurisy. RESULTS: CT findings known to be useful in differentiating tuberculous pleural effusion from empyema (1) contour and extent of pleural thickening, (2) mediastinal pleural involvement, (3)accumulation of extrapleural tissue and (4) change of ipsilateral thoraic volume of empyema. However, none of the above findings were helpful in the differential diagnosis of empyema. CONCLUSION: The differentation of tubrculous pleurisy from pyogenic empyema may be not possible with CT findings only.