Raw Cystic parathyroid adenoma is a rare cause of primary hyperparathyroidism. The authors report one case of cystic parathyroid adenoma, who presented with progressive right hip pain for one year. The patient had severe hypercalcemia at the first presentation and was misdiagnosed as having metastatic cancer at first. An iliac bone biopsy was performed and showed a giant cell tumor. Parathyroid hormone level was evaluated later and was found to be high, 1,555 pg/ml (15-65 pg/ml). An MRI study of the neck was done and revealed a cystic mass 38 x 36 x 40 mm in diameter just below the left lower pole of the thyroid gland. Tc-99m MIBI scan demonstrated increase and retention of radioactivity uptake at the same area. Hyperfunctioning parathyroid gland was considered. Parathyroidectomy was done and histopathology revealed cystic parathyroid adenoma. Serum calcium was normal and hip pain was markedly improved after the surgery.