Cystic parathyroid adenoma is one of the rare causes of hyperparathyroidism, and is usually located in neck and mediastinum. This type of adenoma tends to cause increased serum level of parathyroid hormone and alkaline phosphatase, similar serum calcium level when compared to those of solid adenoma. Thanks to current radioimmunoassay and easy accessibility to serum autoanalyzer, serum calcium level and parathyroid hormone level are more easily measured, which in turn lead to more easier diagnosis of hyperparathyroidism. Also improvement in imaging and nuclear diagnostic method of parathyroid lesion are suggested to enable easy diagnosis of cystic parathyroid adenoma. A 35-year-old male presented with easy fatigability for 12 months. The serum calcium, phosphate, alkaline phosphotase were 11.5mg/dL, 1.4mg/dL, 194IU/L respectively and his parathyroid hormone level in serum was 126.42pg/mL. Neck CT showed enlargement of right lobe of thyroid gland with well defined inhomogenously enhanced density inside the right thyroid gland. The patient was diagnosed of hyperparathyroidim due to parathyroid adenoma and was surgically removed. The surgical biopsy showed cystic parathyroid adenoma. After operation his general condition was improved and serum calcium, phosphate, parathyroid hormone level were normalizd. We report a case of hyperparathyroidism caused by cystic parathyroid adenoma with brief review of literature.