Despite use of computed tomography, some lung cancer patients are found to have unresectable disease at surgery, or they present early with metastases. We studied whether whole-body positron emission tomography (PET) with 18F-fluorodeoxyglucose (18FDG) would improve the preoperative detection of metastases. We retrospectively analysed 34 patients with "operable" non-small-cell lung cancer who underwent 18FDG PET after routine assessment. Management changes produced by the PET scan and confirmatory tests were reviewed. PET identified unsuspected malignant lesions in 10 (29%) patients. Management changes occurred in 14 (41%), including 6 (18%) patients who were changed to non-surgical therapy. These data suggest that whole-body 18FDG PET improves preoperative assessment of lung cancer patients.