Abstract Background: A lung nodule is defined as an approximately rounded opacity more or less well-defined measuring up to 3 cm in diameter. Lung nodules have broad differential diagnosis including neoplastic process, inflammatory conditions, congen-ital diseases, etc. Metastatic lung nodules are among the impor-tant differential diagnoses of pulmonary nodules as the lungs are the second most frequent site of metastases. Pulmonary me-tastases indicate disseminated disease and place the patient in stage W in TNM staging systems which alters the management plan. Conventional radiological methods can provide detailed information about their morphology such as size, location, tis-sue characterization only. Modalities such as CT or MRI could not distinguish between benign and malignant tumors accurate-ly. 18-fluorine fluorodeoxyglucose (F-18 FDG) positron emis-sion tomography-computed tomography (PET/CT) can play an important role in the differential diagnosis of benign and malig-nant lung nodules detected during follow-up. Aim of Study: The aim of this study is to investigate the potential of PET-CT to characterize malignant & benign pul-monary nodules using their standardized uptake value (SUV max) as a measurable unit and size of nodules depending on radiological follow-up and clinical assessment. Patients and Methods: •Those patients were referred to the Radio diagnosis & nuclear medicine departments in el kasr aini Cairo University and pri-vate center for PET CT of the chest over a period of 6 month from July 2021 to January 2022. •This study included 80 patients with positive history of known primary tumor, underwent follow-up study (over period of 6 months) for the most active nodules which are 113 pulmonary nodules (20 solitary, 93 multiple) Results: We retrospectively evaluated pulmonary nodules in 80 patients with positive history of known primary tumor and follow-up to the most active ones which are 113 pulmonary nodules (20 solitary, 93 multiple). The prevalence of malig-nancy of pulmonary nodules in oncological patients was 61/80 (76.2%) with PET/CT provided sensitivity 93.4%, specificity 94.7%. ROC analysis revealed SUVmax cut-off rz 1.475 with significant p-value <0.001. Malignant nodules at follow-up have Mean SUVmax 8.34±6.76, while benign nodules at follow-up have Mean SU-Vmax, 0.58±0.99 with significant p-value <0.001. With Follow -up, we established that benign lung nodules show significant reduction, stable at follow-up or complete resolution. Aim of the Work: The aim of this study is to evaluate FDG PET/CT prognostic performance in pulmonary nodules detect-ed in oncological patients to correctly stage and treat primary cancer saving the patient valuable time. Conclusions: FDG PET/CT is a valuable complementary tool to conventional imaging methods for the evaluation of be-nign and malignant pulmonary nodules to correctly stage and treat primary cancer saving the patient valuable time.