Parathyroid cysts are uncommon lesions of the neck and superior mediastinum, rarely large enough to be of clinical significance. They frequently present as a clinical diagnostic problem. They may mimic solitary thyroid nodule. They can be classified as either functioning or non-functioning depending on whether or not they are associated with hypercalcemia. Non-functioning or “true” cysts are those associated with normocalcemia (85%), whereas functioning or “pseudocysts” are those associated with hypercalcemia (15%). The presence of a high content of intact parathyroid hormone (intact PTH) in the cystic fluid on fine-needle aspiration (FNA), in conjunction with an elevated serum calcium and intact PTH is diagnostic of a functional parathyroid cyst. A functional parathyroid cyst usually requires surgical removal. We report herein one case of functional parathyroid cyst.