Hypercalcemia secondary to cholecalciferol rodenticide toxicosis was identified in two dogs. The first dog died shortly after admission. The second dog responded to treatment with sodium chloride solution, prednisolone, furosemide, and calcitonin. Treatment was needed for a longer period than anticipated and the serum calcium concentration did not stabilize for approximately one month. Although not conclusively demonstrated, calcitonin was considered the cause of severe anorexia. This new class of rodenticides has great toxic potential for dogs, and it is recommended that serum calcium concentration be carefully monitored as treatment for hypercalcemia is gradually withdrawn.