Computed tomography studies are usually used to assess patients with pleural effusions, and radiologists should be aware of the significance of different CT findings for the diagnosis of the effusion. The purpose of this study was to evaluate CT findings for etiological diagnosis of pleural effusions. Contrast-enhanced CT of the chest of 211 patients with pleural effusion of definite diagnosis were evaluated. The CT images were evaluated for the presence and extent of pleural effusion, thickening or nodules, extrapleural fat and other changes in the mediastinum or lung. The CT scans were read by two independent observers and correlation between them was evaluated. Comparison of CT findings between benign and malignant effusions, between exudates and transudates, and between empyemas and the other parapneumonic effusions were carried out. Kappa values for most CT findings were > 0.85. Loculation, pleural thickening, pleural nodules, and extrapleural fat of increased density were only present in exudative effusions. Multiple pleural nodules and nodular pleural thickening were the only pleural findings limited to malignant pleural effusions. The signs were also more frequently seen in empyemas than in other parapneumonic effusions. Computed tomography findings can help to distinguish between transudates and exudates. Although there is some overlap between benign and malignant pleural effusions, pleural nodules and nodular pleural thickening were present almost exclusively in the latter. Although differences between CT findings of empyemas and the other parapneumonic effusions exist, there is no finding which can definitely differentiate between them.