A ten-year-old female spayed Labrador Retriever presented for apocrine gland anal sac adenocarcinoma with regional lymph node metastasis and humoral hypercalcemia of malignancy. At presentation ionized calcium was 2.15 mmol/L (reference range 1.18-1.37 mmol/L). Medical treatment to decrease the ionized calcium was initiated and the following day surgical removal of the primary tumor and metastatic lymph nodes was performed. Following surgery the patient did well and was discharged; however, later developed clinically symptomatic hypocalcemia. The dog was hospitalized for stabilization and calcium was normalized with calcium carbonate and calcitriol. The dog eventually became hypercalcemic once again, but this was resolved by decreasing the doses of, and then discontinuing calcium carbonate and calcitriol.