It is an established entity that thyroid hormones play an important role in mood, behavior, and cognition. Autoimmune thyroiditis, including Hashimoto's thyroiditis (HT), can lead to depression and anxiety disorders. It is thus important to enhance awareness among physicians about this connection to accelerate the diagnostic process. In patients with depression and anxiety disorders, a test for autoimmune thyroiditis should be performed, and in patients with autoimmune thyroiditis, a screening for psychiatric symptoms is necessary. Thus, patients presenting with anxiety or depression disorders should be treated and monitored by both an endocrinologist and a psychiatrist in liaison with each other so as to optimize their management. Moreover, an early recognition of an endocrine condition will help minimize psychiatric morbidity and hence improve health. This chapter explores anxiety, depression, and Hashimoto's disease.