In the past 10 years, positron emission tomography (PET), usually with F-fluoro-2-deoxy-D-glucose (FDG), has become an important imaging modality in patients with lung cancer. FDG-PET is recommended for the diagnosis of indeterminate pulmonary nodules, for which it is significantly more accurate than computed tomography (CT) in the distinction between benign and malignant lesions. A large body of evidence convincingly demonstrates that loco-regional lymph node staging by FDG-PET (in correlation with CT images) is significantly superior to CT alone, with a negative predictive value equal or even superior to mediastinoscopy. FDG-PET also improves extrathoracic staging through detection of lesions missed at conventional imaging or characterization of lesions that remain equivocal on conventional imaging. Ongoing studies now concentrate on more advanced clinical applications, such as the planning of radiotherapy, the response evaluation after the induction of therapy, the early detection of recurrence, and the use in lung cancer screening. Technical innovations, such as PET cameras with better spatial resolution, or new radiopharmaceutical probes to study applications of PET in molecular biology hold promise for future refinements in this field.