PURPOSE: To evaluate the diagnostic accuracy of CT in the differential diagnosis of tuberculous and malignant pleural effusion whether or not lung lesions are present, and to investigate the CT findings used for this differential diagnosis. MATERIALS AND METHODS: This study involved 30 patients with tuberculous pleural effusion (mean age, 44.6 years; M:F=19:11) and 20 with malignant pleural effusion (mean age, 57.2 years; M:F=10:10). All 50 patients underwent enhanced CT chest scans, and the respective conditions were pathologically confirmed. Two radiologists unaware of the pathologic results and distribution of patients reviewed these scans retrospectively and independently. They recorded the presence or absence of helpful lung lesions, CT findings of pleural effusions, their diagnoses, and the degree of confidence of their diagnoses. RESULTS: Among the total of 100 answeres, helpful long lesions were found in 57 cases. Fifty-three of 57 diagnoses (93%) were correct and 26 cases (46%) were diagnosed with a high degree of confidence. Thirty-two of 43 cases (74%) without helpful lung lesions were correct and 11(26%) were diagnosed with a high degree of confidence. All diagnoses made with a high degree of confidence were correct, even in cases without helpful lung lesions. Frequent CT findings in tuberculous pleural effusion included diffuse pleural thickening, enhancement of pleura, deposition of extrapleural fat, and pleural calcification; in malignant pleural effusion, nodular pleural thickening, pleural thickening over 1cm and associated lymphadenopathy were frequent. Mediastinal and circumferential pleural, as well as fissural involvement, were seen in both effusions; there were no statistical differences. CONCLUSION: In most cases, CT provided correct differential diagnosis between tuberculous and malignant pleural effusion. It can help determine the nature of associated lung and pleural lesions, and specific findings of the latter, and can accurately differentiate tuberculous and malignant pleural effusion.