Parathyroid carcinoma accounts for about 0.5%-5% of all parathyroid neoplasms. Very rarely, but if the intrathyroidal parathyroid gland is present, the carcinoma can arise in that developmental anomaly. It is very difficult to distinguish a thyroid nodule from an intrathyroidal parathyroid neoplasm with preoperative radiologic and cytologic evaluations. A 59-year-old male was initially evaluated as presenting a follicular thyroid neoplasm accompanied by hyperparathyroidism. He received hemi-thyroidectomy with central neck dissection and subtotal parathyroidectomy. The final pathology evaluation revealed intrathyroidal parathyroid carcinoma and hyperplasia of contralateral parathyroid glands. We report this very rare and unique clinical situation with a literature review.