We present the case of a severe familial primary hyperparathyroidism related to a germline deletion in the HRPT2 (CDC73) gene. Morphological explorations revealed 2 potential hyperfunctioning parathyroid glands: a left cervical lesion on the neck ultrasound, and an ectopic mediastinal lesion on the parathyroid scintigraphy using Tc-methoxyisobutylisonitrile and on F-fluorocholine PET/CT. Surgery removal and histopathological examination determined that the mediastinal mass corresponded to a thymoma and the cervical lesion to a parathyroid adenoma. Those interesting images illustrate that a thymoma can produce false-positive results both on Tc-methoxyisobutylisonitrile scintigraphy and F-fluorocholine PET/CT.