A 65-year-old woman noticed a rapidly enlarging neck mass with tenderness and complained of dyspnea. She was diagnosed as having anaplastic thyroid carcinoma. She died of respiratory failure 14 days after admission. Marked leukocytosis and hypercalcemia were observed in the clinical course. Both serum granulocyte-colony-stimulating factor and parathyroid hormone-related protein levels were elevated. The cancerous tissue was also immunohistochemically stained for both peptides. We conclude that the leukocytosis and hypercalcemia of this patient were induced by these two factors produced by the tumor.