We report a rare case of thymic Hodgkin lymphoma that occurred in an elderly patient and detected by 18F-FDG PET/CT. A 77-year-old woman with fever of unknown origin underwent 18F-FDG PET/CT scanning, which showed an area of increased radiopharmaceutical uptake in a mediastinal mass corresponding to a thymic lesion at CT scan. On the basis of the PET/CT findings, the patient was referred to surgery with the clinical suspicious of a thymoma. Histological examination demonstrated the presence of a primary thymic Hodgkin lymphoma instead.