Positron emission tomography (PET) is just beginning to emerge as a clinically useful tool in the thorax. Imaging with FDG is used primarily to differentiate benign from malignant abnormalities, including solitary pulmonary nodules, staging bronchogenic carcinoma, and differentiating recurrent tumor from fibrosis following treatment. This article discusses the fundamental properties of PET images, techniques, and current clinical indications in the thorax.