A 10 year-old castrated Keeshond presented for evaluation of hypercalcemia. On initial presentation he was bright and alert and not exhibiting any clinical signs associated with hypercalcemia. His total and ionized calcium concentrations were above the normal reference range; he had a low phosphorus concentration and his PTH level was within normal range. Based on the dog?s signalment, the absence of clinical signs and the results from the blood work, a diagnosis of primary hyperparathyroidism was made. Cervical ultrasonography showed the presence of two enlarged hypoechoic nodules located on contralateral sides of the thyroid gland. The dog was taken to surgery to have both abnormal parathyroid glands removed and the tissues were submitted for histopathology. The histologic diagnosis was a parathyroid carcinoma. This paper will discuss differential diagnoses for hypercalcemia and how to differentiate between these diseases on blood work. It will also include diagnosis of primary hyperparathyroidism, treatment options and complications following treatment.