Current procedures to determine the clinical staging of disease in patients with lung cancer are lacking in accuracy, particularly regarding the presence of metastatic disease. We have evaluated the use of computed tomography (CT) of the chest, brain, and upper abdomen for clinical staging of the extent of disease in 113 consecutive patients with histologically confirmed carcinoma of the lung. Comparisons with mediastinoscopy and surgical findings were made regarding the extent of primary tumor in 47 patients and nodal involvement in 41 patients. The CT scan showed a sensitivity of 86.9%, a specificity of 91.6%, and an accuracy of 89.3% for extrapulmonary extension of the primary tumor and a sensitivity of 50%, a specificity of 96.5% and an accuracy of 82.9% for mediastinal node involvement. Thirty-two of the 85 patients studied by total body CT scan had distant metastasis, of which 24 (75%) were clinically silent. Thus 28.2% of the 85 patients studied had asymptomatic metastatic disease. We conclude that CT of the chest, brain, and upper abdomen is a reliable procedure for staging lung cancer.