A 14-year-old female spayed mixed breed dog presented to the Cornell University Hospital for Animals for treatment of a previously-diagnosed functional parathyroid nodule. The diagnosis of primary hyperparathyroidism was made based on persistent total and ionized hypercalcemia with a normal parathyroid hormone level, as well as a unilateral parathyroid nodule seen on cervical ultrasound. Thoracic radiographs and abdominal ultrasound found no evidence of any other potential cause of hypercalcemia. She was admitted to the hospital and started on vitamin D supplementation to lower the risk of hypocalcemia after treatment. Ultrasound-guided ethanol ablation was used to destroy the autonomous parathyroid tissue. Ionized calcium levels decreased slowly over the next 4 days after ablation to the upper end of normal. Two months after ablation, calcium remained in the high-normal to mildly increased range, which is a common finding during vitamin D supplementation.