The prevalence of iron deficiency anemia has decreased in recent years because of improved dietary habits. Yet, iron deficiency anemia is still the most common anemia. Among mature adults, anemia of chronic disease is probably more common. Mean corpuscular volume and red cell distribution width, along with a peripheral smear examination, can often distinguish iron deficiency anemia from other common microcytic anemias, such as thalassemia minor. A normal serum iron level excludes iron deficiency anemia and indicates other causes for microcytic anemia. Often, a low serum iron level and total iron-binding capacity are due to chronic disease, and measurement of serum ferritin or a bone marrow stain for hemosiderin will be necessary to diagnose iron deficiency. Iron therapy to restore the red cell mass should be continued until iron stores are replenished.