Megaloblastic anemia in children is mainly due to folic acid or vitamin B12 deficiencies. However dosages of these two vitamins must be performed before any vitamin supplementation or blood transfusions are given in order to establish precisely the etiologic diagnosis. A disorder in the metabolism of these vitamins must be considered in any infants in whom the onset of neurological abnormalities is associated with the characteristic hematological abnormalities. Imerslund's syndrome is a specific vitamin B12 malabsorption defect that warrants consideration as it is easy to recognize on the basis of the association of megaloblastic anemia and proteinuria. A possible drug-induced etiology must also be looked for. In the absence of vitamin deficiency, several rare etiologies must be considered. A macrocytosis, occasionally with megaloblastosis reflecting an abnormal erythropoiesis, may accompany an hemopathy, eventually malignant.