Parathyroid carcinoma is unusual and its intrathyroidal variant is extremely rare. Therefore, few cases have been reported to describe a case of parathyroid carcinoma located inside the thyroid gland. The case corresponds to a 14-year-old girl who came to the office with a severe osteoarticular disease, depression, calcemia of 14.3 mg/dl and parathyroid hormone of 2,792 pg/ml. Right neck exploration was conducted and a parathyroid carcinoma was found located intrathyroidally. A right thyroid lobectomy was performed. A 20-month follow-up period revealed no recurrence of clinical or biochemical signs. In patients with severe hypercalcemia and significant elevation of parathyroid hormone, the diagnosis of parathyroid carcinoma has to be considered. It is worth highlighting the early age of presentation in this case. Treatment has allowed the effective control of the disease and its recommended long-term follow-up.