The dissemination of positron emission tomography (PET) technology has enabled a functional approach to the evaluation of lung cancer that complements the anatomic assessment provided by chest radiography, computed tomography (CT) scanning, and magnetic resonance imaging. PET has excellent sensitivity and good specificity for the determination of malignancy in the solitary pulmonary nodule, but these data must be weighed against the evidence of instances of false-positive results because of inflammatory lesions and false-negative results in small- or low-metabolism neoplasms. Therefore, PET may not be advisable when these scenarios apply. Furthermore, in a patient with a very high pretest likelihood of lung cancer (eg, a new or enlarging spiculated nodule in a long-time smoker), the value of PET is less certain because a negative result may be discounted. PET has altered the approach to the staging of lung cancer. It adds value to the evaluation of the mediastinum and extrathoracic structures compared to conventional methods by upstaging or downstaging a substantial proportion of patients. If the staging assessment is negative on PET, the use of mediastinoscopy may be obviated in selected cases. Histologic confirmation of positive PET findings should be obtained before excluding patients from curative resection. PET provides incremental information to CT in the evaluation of persistent and recurrent disease, and response measured on PET appears more accurate as a predictor of ultimate survival. The more recent development of PET-CT permits fusion of anatomic and functional information. Early investigations suggest that this strategy provides superior results compared to either technique alone.