Objective: 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) not only givesinformation about anatomical features of lung lesions but also about their metabolic activity. This study aimed to determinethe mediastinal and parenchymal pathologies of the lung with false-positive FDG involvement and characteristics that couldbenefit differential diagnosis. Materials and Methods: This study retrospectively analyzed 1,924 subjects that underwent 18F-FDG PET/CT from Decem ber 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 inflam matory events, and organized pneumonia (OP) were 64 (45%), 36 (25%), and 18 (13%) cases, respectively, in order offrequency. The median SUVmax value of all lesions was 5.2 (min–max, 2.5–37.6). Moreover, mediastinal lymph node involve ment 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 indeveloping countries. 18F-FDG PET/BT is an unreliable method for the differential diagnosis of benign diseases characterizedby inflammation. Thus, metabolic activity evaluation is more suitable