A 66-year-old woman was admitted to our hospital with difficulty in walking. Magnetic resonance imaging revealed mass lesions at T2- T3 vertebrae causing deviation of the spinal cord. The positron emission tomography (PET) scan of the body showed a hypermetabolic state in the right maxillary sinus and multiple metastatic lesions in the skeletal system indicating a metastatic tumor of unidentified origin. The patient was operated immediately for cord compression that could lead to a neurological problem. Pathological examination of the operation specimen was consistent with a giant cell tumor. The patient's serum calcium level was elevated (11.6 mg/dL; reference limits: 8.5-10.5) and phosphorus level was below the normal ranges. Parathyroid hormone was extremely high; 2097 pg/mL (reference limits: 15-65 pg/mL). Sonographic examination of the neck revealed multinodular goiter and a lesion at the inferior region of the right thyroid lobe suggesting a parathyroid adenoma. Skeletal X-rays suggested Brown tumors of long bones. The case was diagnosed as primary hyperparathyroidism and was referred for parathyroidectomy.