Endocrinopathies abound as our discussion continues to the thyroid gland. We will discuss hyperthyroidism (primarily in cats) and hypothyroidism (primarily in dogs)- both in stable and critical case scenarios. The pathophysiology of these disease processes, how it can affect the patient, signalment, clinical signs and presentation, testing, lab processing and handling, stabilization and treatment of these commonly seen patients will be discussed in a case-based format.