Aims We have evaluated the efficacy and clinical impact of FDG-PET for staging patients with potentially respectable non-small cell lung cancer (NSCL) in CT. Materials and methods We have prospectively studied 115 patients (104 M/11 F and mean age: 59 years old) with diagnosis of potentially resectable NSCL, (resectable criteria: Stage < IIIB in CT), including cases with equivocal lesions in mediastinum or in extrathoracic sites. In all patients we have done a whole body scan with FDG-PET, after intravenous injection of 370-440 MBq of 18F-FDG, in normoglucemia conditions. A qualitative and semiquantitative (SUV) analysis of images was carried out. Results Prevalence of mediastine lymphatic metastasis was 46.6 %, and CT was false negative (FN) in 21 cases and FDG-PET only in 9. Overall sensitivity, specificity, negative predictive value, positive predictive value and accuracy were of 83.3, 73.7, 75, 81.8 % and 78.3 % in FDG-PET, and 61.1, 68.8, 64.7, 65.6 % and 65.2 % in CT, respectively. All contralateral or supraclavicular lymph metastasis (N3) were detected in FDG-PET, whereas CT had 7 FN cases. In distant metastasis, FDG-PET had 1 FN and 4 FP, whereas CT had 6 cases FN and 10 FP. Clinical Impact of FDG-PET was 26 % of patients, avoiding surgery in 11 cases, allowing in 8, indicating neoadjuvant chemotherapy in 8 and surgery of synchronic incidentaloma in 3 cases. Conclusion . PET-FDG had better efficacy than CT in respectable NSCL, and should be incorporated in diagnosis protocols of NSCL before surgery decision making.