PURPOSE: To evaluate whether or not previously known CT criteria for differentiating malignant and benign pleural diseases are useful in the differentiation of diffuse malignant pleural diseases and tuberculosis. MATERIALS AND METHODS: We retrospectively analyzed CT scans of 42 patients comprising 20 cases of malignant pleural diseases and 22 cases of tuberculous pleural diseases, according to previously known CT criteria for differentiating malignant and benign pleural diseases. RESULTS: The most common shape of pleural effusion was crescentic in malignant pleural diseases and loculated in tuberculosis. The aggressive nature of pleural effusion, pleural rind, and pleura thickenign was 1.5 times more frequently observed in malignant pleural diseases than in tuberculosis. Smooth thickening or smooth nodular pleural thickening and extrapleural deposition of fat were 1.5 times more frequently found in tuberculous than in malignant pleural diseases. Interruption of pleural thickening was found twice as frequently in malignant pleural diseases as in tuberculosis. Decreased lung volume was found twice as frequently in tuberculous as in malignant pleural diseases. Anatomical mediastinal pleural involvement was three times, and irregular nodular pleural thickening nine times more frequent in malignant pleural diseases than in tuberculosis. The sensitivity and specificity of CT findings above 70%, and thus suggesting malignant pleural diseases, were as follows: 1) aggressive nature of pleural fluid collection extending to the azygoesophageal recess or tongue of the lung (51.5%, 75%); 2) involvement of anatomical mediastinal pleura (69.2%,73.7%); 3) irregular nodular pleural thickening (87.5%, 69%). CONCLUSION: Although there in overlap between previously known CT criteria for the differentiation of benign and malignant pleural diseases, the aggressive nature of pleural fluid collection extending to the azygoesophageal recess or tongue of the lung, the involvement of anatomical mediastinal pleura and irregular nodular pleural thickening may suggest malignant pleural diseases.