We report a case of a false-positive finding in FDG PET/CT following radiotracer extravasation. A 15-year-old male patient was referred for therapeutic evaluation status post-chemotherapy for a lymphoblastic lymphoma. FDG PET/CT showed discordant findings with a marked decrease in a liver/hepatic hilum uptake, disappearance of a subcutaneous left supraclavicular uptake, and appearance of intense right axillary nodal uptake. Extravasation in the right superior limb was noted. Comparison with the previous scan showed that the axillary nodes were present, measured less than 1 cm in their short axis, had not increased in size, and had a fatty hilum. We concluded that FDG uptake was caused by a migration in lymphatic vessels.