Because anemia is a condition rather than a disease, an underlying cause must be determined when anemia is identified. Microcytic anemia is a common category of anemia. Iron deficiency anemia is the most common type of microcytic anemia and is also the most common anemia. The clinical presentation of anemia varies according to its severity. Anemias resulting from chronic disease and thalassemia are also relatively common types of microcytic anemia and should be differentiated from iron deficiency to avoid repeated unnecessary trials of iron therapy. Low serum ferritin is the best single laboratory parameter for the diagnosis of iron deficiency. Serum iron, total iron binding capacity and hemoglobin electrophoresis, if necessary, can help differentiate the type of microcytic anemia in patients with normal or elevated levels of serum ferritin. If the evaluation identifies iron deficiency as the type of anemia, the underlying cause must be investigated.