The parietal pleura bordering pleural space collections was analyzed with computed tomography (CT) in 35 patients with thoracic empyema, 30 patients with malignant effusion, and 20 patients with transudatory effusion. Enhancement of the parietal pleura was present in 96% of the 25 patients with empyema who underwent contrast material-enhanced examinations. Of the 35 patients with empyema, 86% showed thickening of the parietal pleura, 60% showed thickening of the extrapleural subcostal tissues, and 35% showed increased attenuation of the extrapleural fat. None of the 20 patients with transudatory effusion showed these findings. Of the 30 patients with malignant effusion, eight patients (27%) showed chest wall changes similar to those of the patients with empyema. However, two-thirds of these patients had a recognized superimposed complication (ie, sclerotherapy). Contrast-enhanced CT appears to be sensitive to chest wall changes in patients with empyema. CT study of the parietal pleura may help suggest occult pleural space infections and may influence therapeutic decisions that vary with the stage of empyema.