Although 18F-FDG-PET is very sensitive for a variety of malignancies, it can lack specificity. In addition to malignant tissue, any active infectious or inflammatory process can demonstrate FDG avidity. We report 3 patients with different types of cancer who had abnormal 18F-FDG uptake on PET scan caused by tuberculous lymphadenitis. All were found to have incidental multiple lymph adenopathies with increased FDG uptake on PET scan. All three patients were proved to have tuberculosis lymphadenitis by pathologic examination and were successfully treated with anti-tuberculous therapy.