Cystic parathyroid adenoma is one of rare causes of hyperparathyroidism, and tends to cause increased serum level of parathyroid hormone, alkaline phosphate and serum calcium level similar to when compared to those of solid adenoma. The possibility of a coincidental appearance of primary hyperparathyrodism and nonmedullary thyroid cancer is rare, and often neglected. A 40-year-old female presented with constipation and weight loss for 3 months. The serum calcium, phosphate and alkaline phosphate were 16.6 mg/dl, 2.2 mg/dl and 505 IU/L respectively and serum parathyroid hormone level was 1556.2 pg/mL. Neck US showed mixed nodules at both thyroid lobes, and PET-CT showed a right thyroid nodule without FDG uptake. The patient was diagnosed of primary hyperparathyroidism and underwent parathyroidectomy and a total thyroidectomy. Histopathologic results revealed parathyroid adenoma with cystic change (2 cm greater diameter) in the right lower parathyroid gland and coexistent papillary carcinoma of the right lobe of thyroid gland (infiltrating, 0.3 cm in greater diameter). She remained well and serum calcium, phosphate, parathyroid hormone level were normalized within 24 hours.