Herein, we present a rare case of PHPT due to ectopic intrathymic parathyroid adenoma in a 15-year-old girl, which was incidentally diagnosed based on laboratory abnormalities and successfully managed only after the reoperation with VATS thymectomy in experienced hands after a 3-month postoperative course of persistently elevated PTH and hypercalcemia and continued presence of thymic adenoma following the initial unsuccessful parathyroidectomy. This evidence concerns the gene PTH and parathyroid gland adenoma.