Glycolysis is increased in tumor tissues. [18F]fluoro-2-deoxy-D-glucose (FDG) is a glucose analogue radiopharmaceutical used in positron emission tomography (PET) to trace glucose metabolism. We investigated the sensitivity and specificity of FDG-PET imaging in the diagnosis and staging of lung cancer. One hundred and seven patients who had abnormal chest roentgenograms underwent whole-body PET imaging using FDG. PET scan results were classified as positive or negative based on the presence or absence of increased FDG uptake in the lung and/or in the mediastinum. All 82 patients with lung cancer had increased FDG uptake in the lungs, whereas only 12 of 25 patients with nonmalignant diseases had increased FDG uptake. Sixteen lung cancer patients with mediastinal metastases had increased FDG uptake in the mediastinum, of whom three had no lymphadenopathy on computed tomography of the chest. Sixteen lung cancer patients without mediastinal nodal involvement had no FDG uptake in the mediastinum. Seven of these patients had lymphadenopathy on computed tomography. FDG-PET imaging is 100% accurate in predicting mediastinal involvement in patients with lung cancer. It is 100% sensitive and 52% specific in predicting the malignant nature of a chest radiographic abnormality.