Non anemic iron deficiency (NAID) is the most common nutritional deficiency. Symptoms more frequently observed in children and adolescents include fatigue, delayed psychomotor development as well as decreased school and athletic performances. Iron treatment is effective in improving symptoms in older children and adolescents. In children under 2 years of age, there is currently no evidence of the efficacy of substitution therapy on development. Preemptive treatment is not justified considering the available evidence beyond premature or small newborns for gestational age and should only be initiated if a diagnosis of iron deficiency is confirmed. Oral iron supplementation is the first-line treatment of NAID.