Insulinoma is a rare disease of dogs, yet it is recognized as the most common islet cell tumor of the endocrine pancreas. Dogs with insulinomas often have similar clinical signs and clinical pathology data, making a presumptive diagnosis easier for a veterinarian. Arriving at a definitive diagnosis, however requires both surgery and histopathology. Veterinarians, therefore, must be aware of the biologic behavior of the tumor, the typical clinical signs and clinical pathology data, treatment options and prognostic factors in order to warrant the search for a definitive diagnosis.