A 17-year-old girl underwent 18F-NaF PET/CT to evaluate bone pain after an accident. The images did not identify any osseous lesion. However, there was a focally increased activity in the left upper chest, which corresponded to a partially calcified soft tissue mass in the mediastinum, suggestive of malignancy. The result led to subsequent 18F-FDG PET/CT imaging, which demonstrated intense activity in the mediastinal mass and in multiple cervical, supraclavicular, and mediastinal lymph nodes. Hodgkin lymphoma was diagnosed histopathologically following the biopsy.