The helpfulness of 18F-2-deoxyglucose positron emission tomography (FDG-PET) in restaging non-small cell lung cancer (NSCLC) has not been extensively evaluated. A total of 156 patients referred for restaging of NSCLC were retrospectively evaluated. According to the classification of American Joint Committee on Cancer, stages I and II were defined as conventionally resectable, stage IIIA as locally advanced but resectable, stage IIIB as locally advanced but unresectable, and stage IV as absolutely unresectable. Compared to initial staging by chest computed tomographic findings, FDG-PET down-staged 45/156 (29%) and up-staged 52/156 (33%) NSCLCs. In addition, 37/156 (23%) patients were reclassified from resectable to unresectable and 22/156 (14%) patients were reclassified from unresectable to resectable. Our results prove the helpfulness of whole body FDG-PET for restaging NSCLC.