Anemia is defined as a hemoglobin level that is two standard deviations below the mean for age. After children reach the age of 12, the hemoglobin norm can be further divided into gender-specific ranges. When a patient presents with anemia, it is important to establish whether the abnormality is isolated to a single cell line [red blood cells (RBC) only] or whether it is part of a multiple cell line abnormality. In children, anemia is usually caused by decreased RBC production or increased RBC turnover. Anemia is usually classified based on the size of RBC (microcytosis, normocytosis, or macrocytosis) as measured by the mean corpuscular volume. Although iron deficiency anemia is usually microcytic, some patients may have normocytic blood cells. From a practical point of view, it is better to use in children the etiologic classification of anemia which includes impaired red cell formation, blood loss and hemolytic anemia. Most children with anemia are asymptomatic, and the condition is detected on screening laboratory evaluation. Iron deficiency can be treated with oral iron, intravenous iron, and/or blood transfusion, depending on the patient`s hemoglobin levels, tolerance and co-morbidity. Oral iron salts are usually the first line of treatment for uncomplicated iron deficiency, but are poorly absorbed and lead to gastrointestinal side effects. In some cases, iron refractory iron deficiency anemia (IRIDA), a hereditary recessive anemia refractory to oral iron, occurs. IRIDA shows a slow response to intravenous iron and partial correction of anemia.