A case of carcinoma of the parathyroid gland causing hyperparathyroidism was experienced at the department of orthopaedic surgery, C.A.F.G.H. This patient, a 23 years old male, had complained of a left shoulder pain during the past 3months. And weakness of the lower extremities causing walking disturbance, multiple bone pain, and polyuria had occurred sinoe one month before admission. Physical examination revealed a hard palpable mass in the right anterior region of the neck. Radiologic examination revealed subperiosteal bone resorption in phalanges of the hands and feet, generalized osteoporosis and cystic lesions, and pathologic fracture of the ribs, left humerus, and left femur. Laboratory studies demonstrated hypercalcemia, hypophosphatemia, increased alkaline phosphatase and PTH, hypercalciuria, and hyperphophaturia. Sonogram and C-T scan of the neck revealed a mass in the right inferior portion of the thyroid. Rib biopsy revealed the findings of ostitis fibrosa cystica, and parathyroid gland and regional lymph node biopsy revealed a parathyroid carcinoma with regional lymph node metastasis.