An 11 year old, male castrated, mixed breed dog that presented to the Cornell Oncology Service for a functional thyroid carcinoma. The patient was exhibiting clinical signs consistent with hyperthyroidism such as polyphagia, polyuria, polydipsia, weight loss, poor body condition and hypertension. A mass was present on the ventral neck and was surgically excised with no complications peri-operatively. The patient recovered uneventfully from general anesthesia and surgery and is reportedly doing well at home.