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Objective: 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) not only gives information about anatomical features of lung lesions but also about their metabolic activity. This study aimed to determine the mediastinal and parenchymal pathologies of the lung with false-positive FDG involvement and characteristics that could benefit differential diagnosis. Materials and Methods: This study retrospectively analyzed 1,924 subjects that underwent 18F-FDG PET/CT from December 2010 to January 2015. Subjects with a maximum standardized uptake value (SUVmax) value of =2.5 in the lung tissue, mediastinal lymph nodes with no primary lung malignancy, and a benign pathology result were included. Results: The mean age of the 143 subjects was 61.7±11.0 years. The pathologies anthracosis, granulomatous inflammatory events, and organized pneumonia (OP) were 64 (45%), 36 (25%), and 18 (13%) cases, respectively, in order of frequency. The median SUVmax value of all lesions was 5.2 (min-max, 2.5-37.6). Moreover, mediastinal lymph node involvement was frequent (59%). The median SUVmax value of anthracotic lesions was significantly lower than the median SUVmax value of granulomatous and OP lesions (p<0.001 and p=0.007, respectively). No significant difference in the median SUVmax value was noted between granulomatous and OP lesions. Conclusion: Anthracosis and tuberculosis should be considered as benign causes of mediastinal lymph node positivity in developing countries. 18F-FDG PET/BT is an unreliable method for the differential diagnosis of benign diseases characterized by inflammation. Thus, metabolic activity evaluation is more suitable. [ABSTRACT FROM AUTHOR]