We report an analysis of computed tomography (CT) of the thorax in 75 patients with combinations of pleural and parenchymal disease or complex pleural shadows. These patients were among more than 300 with pulmonary disease examined by this method. Twenty-eight percent of the 75 scans within this group were classified as high value, contributing information which was not available from other clinical or roentgenographic data, and which directly altered the management, diagnosis, or prognosis of these patients. Forty percent of the scans were classified as of intermediate value, contributing to better understanding of the case but with no major influence on patient management or prognosis. Thirty-two percent of the scans added no additional information to the chest roentgenograms. Thirty-seven percent of the 46 scans done specifically to differentiate pleural from parenchymal disease were classified as of high value, but only 14% of the scans in patients with pleural fluid loculations or pleural masses were placed in this category. We conclude that thoracic CT provided information not otherwise available in one third of the patients with complex combined pleural and parenchymal disease examined in our series.