Background: Chronic Osteomyelitis is an infection of bone and bone marrow. Diagnosis is based mainly on correlation between history, clinical picture, lab analysis, bacteriological, pathological, and imaging studies. Bone biopsy for culture and sensitivity is the gold standard for the correct identification of the causative organism. The present retrospective study aims to evaluate the accuracy of FDG PET-CT in the diagnosis of COM. Methods: 18 patients who underwent FDG-PET/CT scanning for clinically or radiologically suspected COM of the lower extremity. Patients were 16 males and 2 females.14 patients had septic nonunion, 3 patients with aseptic nonunion, and 1 with chronic diffuse sclerosing OM of Garre. 7 patients had implants at site of examination at the time of scan. Diagnosis of COM was confirmed by surgical deep cultures and pathological analysis following PET/CT scanning. FDG-PET uptake was measured by SUV max, and we compared SUV max at the infected site and at the contralateral side (SUV ratio). Results: the sensitivity, specificity, accuracy, PPV and NPV of PET SUV max were 100%, 66.7%, 94.44%, 93.75% and 100% respectively in diagnosis of COM at a cut-off value of (4.46). The present study included 15 true positive, 2 true negative and 1 false-positive PET/CT results. Conclusion: 18F-FDG PET/CT is a highly sensitive and specific method for the evaluation of chronic osteomyelitis in patients with or without trauma. PET/CT provides anatomical localisation and characterization of the infected area and has a very important role in preoperative planning with a high degree of accuracy.