Correctly staging lung cancer is extremely important because the treatment options and the prognosis differ significantly by stage. Several noninvasive imaging studies are available to aid in identifying disease both within and outside of the chest. Chest CT scanning is useful in providing anatomic detail that better identifies the location of the tumor, its proximity to local structures, and whether or not lymph nodes in the mediastinum are enlarged. Unfortunately, the accuracy of chest CT scanning in differentiating benign from malignant lymph nodes in the mediastinum is unacceptably low. Whole-body positron emission tomography (PET) scanning provides functional information on tissue activity and has much better sensitivity and specificity than chest CT scanning for staging lung cancer in the mediastinum. In addition, metastatic disease can be detected by PET scan. Still, positive findings of PET scans can occur from nonmalignant etiologies (eg, infections), so that tissue sampling to confirm the suspected malignancy must be performed. The clinical evaluation tool, which is composed of a thorough history and physical examination, remains the best predictor of metastatic disease. If the findings from the clinical evaluation are negative, then imaging studies such as a CT scan of the head, a bone scan, or an abdominal CT scan are unnecessary, and the search for metastatic disease is complete. If signs, symptoms, or findings from the physical examination suggest the presence of malignancy, then sequential imaging, starting with the most appropriate study based on the clues obtained by the clinical evaluation, should be performed. Abnormalities detected by all of the aforementioned imaging studies are not always cancer. Unless overwhelming evidence of metastatic disease is present on an imaging study, in situations in which it will make a difference in treatment, all abnormal scan findings require tissue confirmation of malignancy so that patients are not precluded from having potentially curative surgery.