Thyroid hormones generally stimulate erythropoiesis. These agents also increase erythrocyte 2,3-DPG concentrations, which serve to enhance the delivery of oxygen to tissues. In the absence of thyroid hormones, anemia frequently develops and may be normocytic, hypochromic-microcytic, or macrocytic. Anemia is an uncommon finding in hyperthyroidism but when present may be morphologically similar to that observed in hypothyroidism. Pernicious anemia has been strongly associated with hypothyroidism, hyperthyroidism, and thyroiditis. Complete correction of anemia often requires restoration of thyroid function as well as specific hematinic therapy. Continued attention to hematologic status is essential in the management of patients with thyroid diseases.