Lung cancer is the leading cause of death from cancer in both men and women. The presence of distant metastases or metastases to mediastinal lymph nodes has a significant effect on prognosis. Clinical examination and the use of noninvasive studies such as CT scan and bone scan are currently used for staging patients with non-small cell lung cancer. Positron emission tomography (PET) with [18F1 fluoro-deoxyglucose (FDG) can detect increased glucose metabolism characteristic of malignant tumors. PET has been shown to have an accuracy of >90|X% when it is used to determine whether a lung nodule is malignant or benign. Studies with whole-body PET imaging have detected clinically occult metastases, undetected by other noninvasive studies, in a significant percentage of patients. Because mediastinal lymph nodes are easy to access either at the time of thoracotomy or by cervical mediastinoscopy, significantly more data are available regarding the utility of PET for the detection of mediastinal lymph node metastases in patients with non-small cell lung cancer. A number of studies confirm that PET plus CT is more accurate than CT alone at predicting the presence or absence of mediastinal lymph node metastases. A decision analysis has recently been published describing the use of PET for mediastinal staging of the patient with non-small cell lung cancer. Clinical trials are under development to determine the exact role of PET for detecting both distant metastases and mediastinal lymph nodes.