Positron emission tomography (PET) is a imaging technique which identifies abnormalities by utilising their metabolic properties rather than their anatomical density. In this study, we evaluated the place of PET scanning for the characterisation of additional abnormalities discovered on routine, preoperative CT evaluation of patients with proven NSCLC. A total of 21 patients underwent PET scanning using fluorodeoxyglucose (FDG). In these patients, routine CT scans had found 26 concomitant lesions which were in lung, adrenal gland, liver, kidney, spleen and pleura. FDG uptake was positive at the primary site in all patients. FDG uptake in 13 of the concomitant lesions suggested malignancy. Malignancy was confirmed at all of these foci by histology in eight (six at thoracotomy, fine needle aspiration biopsy (FNAB) and open biopsy) and by clinical and radiological follow-up for 1-15 months in five. In 13 lesions, PET suggested benign disease. Histology reported no evidence of malignancy in five and the six foci followed on clinical and radiographic follow-up for 2-16 months had no evidence of malignancy. PET was falsely negative in only one site where malignancy was proven by thoracotomy. PET failed to detect the remaining lesion which was an unassociated primary kidney tumour in a patient with Li-Fraumeni syndrome. The accuracy of PET scanning in the assessment of those additional lesions found on CT evaluation of otherwise operable NSCLC was found to be 96% with a sensitivity of 93% and specificity of 100%. These results indicate that PET is useful to characterise additional lesions found on CT scan of patients with NSCLC.