A 16-year-old girl, with known medullary carcinoma of the thyroid, presented with a borderline elevated serum calcitonin level of 13.1 pg/mL (normal range, 0–11.5 pg/mL). CT scan of the thorax revealed multiple lobulated, slightly hyperdense soft tissue masses in both breasts reported likely to be multiple fibroadenomas; a suspicion of metastatic deposits was also raised. Whole-body FDG-PET demonstrated multiple foci of FDG uptake of varying degree in both breasts. A delayed limited PET showed a drop in FDG uptake as demonstrated by standardized uptake values. Based on the FDG uptake, the borderline elevated serum calcitonin level and the fact that breast metastases from medullary carcinoma of the thyroid, although rare, has been reported, excision biopsy of the 3 most prominent foci were carried out. On histopathologic examination, the tumors were encapsulated and showed a biphasic pattern. The morphology was that of a juvenile or cellular fibroadenoma with cellular fibroblastic stroma that lacked the specialized myxoid stroma around lobules seen in conventional fibroadenomas. The present finding in this unusual case study of multiple juvenile fibroadenoma is an interesting addition to the literature of potential false-positive FDG-PET studies and to the differential diagnosis of multifocal FDG uptake in breasts in young patients.