Abstract Background: In case of multiple pulmonary and extrapul-monary lesions, it is difficult to determine if the lung mass was primary lesion or metastasis from a distant organ, even in multiple pulmonary lesions. it is difficult to determine sit of primary one. Aim of Study: We retrospectively measure the SUVmax and D  SUVmax in pulmonary and extrapulmonary lesions and identify if there is a cutoff value of SUVmax between patho-logically proved synchronous second primary and metastatic lesions. Patients and Methods: 65 patients (50 male and 15 female with age ranged from 35 to 70 years) who had multiple pulmonary and extrapulmonary lesions were evaluated by PET/CT, all patients were evaluated by oncology physicians, patients were selected after histopathological evaluation, patients with lung metastasis taken as a control group. SUVmax and D  SUVmax were measured in both groups. Results: A significant (DSUV) max difference between both included groups: Metastatic lung cancers and second primary lung tumours with a cutoff value of 35% while no significant DSUVmax between the studied cases in the same groups, as below this level approved for metastatic lesion and above this cutoff values consistent with the synchronous second primary tumour, this help in better staging and man-agement of lung cancer. Conclusion: PET CT is considered as a functional non-invasive technique, we recommended that all patients with multiple pulmonary and extrapulmonary lesions to add this investigation, before taking the decision of management, it can differentiate between multiple primaries and metastatic lesion depending upon the FDG activity.