Parathyroid cyst (PC) is a very rare condition. A case of intrathyroidal PC is being reported here in a 53-year-old woman who presented to the endocrine clinic with slowly progressive painless left anterior neck swelling for 1 year with no symptoms of thyroid or parathyroid dysfunction and no compressive symptoms. Ultrasound of the thyroid showed a well-defined cystic lesion measuring 4.7 × 3.6 cm in maximum diameter with internal echoes within the cyst located in the left lobe of the thyroid gland. Fine needle aspiration revealed colorless clear fluid with a high concentration of parathyroid hormone. The patient underwent left hemithyroidectomy at her request. Histopathology revealed parathyroid tissue with unilocular cyst and thyroid tissue with goitrous changes. She was in remission, and there was no evidence of thyroid or parathyroid dysfunction after surgery.