Hyperparathyroidism is a diagnosis that is made on the basis of an imbalance in normal homeostatic processes regulating calcium concentrations in the body. Over time this diagnosis has taken on new subtleties such as normocalcemic hyperparathyroidism and normohormonal hyperparathyroidism. Beyond these intricacies of diagnosis, preoperative localization is aided by a number of modalities including nuclear medicine sestamibi imaging. It should be acknowledged that sestamibi was first used by cardiologists assessing myocardial perfusion and only later was its application for parathyroid localization appreciated. This fact illustrates that tissues other than parathyroid demonstrate sestamibi uptake. Herein we present the case of a 55 year-old female who presented to our office on referral from endocrinology for a presumptive diagnosis of normocalcemic hyperparathyroidism. During the course of this patient's workup her localization studies strongly suggested the presence of ectopic parathyroid tissue within her anterior mediastinum. Both Sestamibi and 4-D CT imaging were concordant on this issue and she was thus referred to Thoracic Surgery for thoracoscopic excision. However, once these lesions were removed, intraoperative PTH assays failed to decline as predicted and final pathology confirmed that a thymoma rather than parathyroid tissue had be excised. She subsequently recovered and underwent a second workup where abnormal parathyroid tissue was localized within the neck and ultimately removed through a traditional cervical approach. This case serves to underscore the biologic reality that other pathologic entities are sestamibi-avid and must be considered particularly when potential ectopic parathyroid tissue is sought.