Hypercalcemic crisis, generally accepted as serum calcium concentration greater than 3.5 mmol/L,constitues a life-threatening endocrinologic emergency,and is most frequently caused by either primary hyperparathyroidism (PHPT) or malignant diseases.Parathyroid cysts are uncommon lesions, most of that are located in the low part of the neck. By routine neck ultrasound scan investigation in a large series of 6621 patients, only 5 parathyroid cysts were detected, yielding a prevalence of 0.075% in setting of unselected patients.The parathyroid cysts in the mediastinum are much less frequently encountered, with only 106 cases reported in English literature.2,3 Moreover, less than half of these cases presented as functional with elevated serum calcium and parathyroid hormone, and only 10 cases were associated with hypercalcemic crisis.3 Herein, we present a rare case of mediastinal parathyroid cyst associated with recurrent hypercalcemic crisis, which diagnosed by ultrasound-guided fine needle aspiration (FNA).