We report herein the case of a 48-year-old man with long-term persistent primary hyperparathyroidism (pHPT) despite undergoing a parathyroidectomy in 1976, followed by a reoperation in 1978, for whom resection of a parathyroid adenoma in the upper mediastinum was eventually performed. His postoperative course was complicated by recurrent hypocalcemia refractory to oral calcium substitution and significantly elevated levels of parathyroid hormone (PTH). The radiological findings are presented, and we discuss the possible reasons for the coincidence of severe hypocalcemia with increased PTH levels in association with pHPT.