A 9 year old castrated male Labrador Retriever presented to the Cornell University Hospital for Animals (CUHA) with a 1 year history of intermittent weakness, collapse, and 2 generalized seizures. The dog had documented hypoglycemia and hyerinsulinemia during these episodes as well as relief of clinical signs after glucose supplementation. On presentation to CUHA, physical examination revealed a mildly over-conditioned (BCS=7/9) dog with iris cysts OU. Blood glucose concentration was 42 mg/dL (reference range 60-120 mg/dL). Based on the patient's history and elevated amended insulin:glucose ratio, an insulinoma was presumptively diagnosed. Initial management with nutritional modification and exercise restriction failed to adequately control clinical signs, so surgical removal of the insulinoma along with excision of two liver nodules (metastatic insulinoma) was performed. Persistent hypoglycemia prompted additional medical management of diazoxide and prednisone. The purpose of this case report is to characterize the common clinical presentation, diagnosis, treatment, and prognosis of canine insulinomas.