Metabolic imaging studies are an integral part of oncology practice, particularly with 18 fuorodeoxyglucose PET scanning. Lung cancer is one of the primary indications of a PET/CT study. It is helpful in staging, evaluating treatment response and follow-up of these patients. The recent development of PET/CT, which incorporates a multislice CT scanner to the PET detector, improves results, combining metabolic information from the PET with anatomic data obtained with CT. It reduces false positive results from PET in cases of inflammatory disease such as pneumonia or Drug reactions, which are frequent in this group of patients. These conditions are easily recognized by CT. It also improves the detection of primary tumors, when they are adjacent to atelectasis or desmoplastic reactions. PET-CT studies are able to characterize the metabolism of mediastinal and hilar lymph nodes, thus obviating the need for further related imaging studies or invasive procedures. In the assessment of metastatic disease, it allows a whole body analysis in only one study, with high predictive value and optimal cost-benefit relation. The detection of a second primary tumor is not infrequent in these patients. PET-CT is useful in the evaluation of treatment response after chemotherapy, and for the long term follow-up.