The leukemoid reaction is defined by the presence in peripheral blood of white cells above 50,000/mm3 or neutrophils above 30,000/mm3 . The frequency varies between 1.3 and 15% of newborns admitted to neonatal intensive care units [1]. It usually appears during the first two weeks of life and more frequently during the first four days, the duration is about 8.5 days [2]. In extremely premature, this process is produced by an inflammatory response that active cytokines who increased granulocyte colony-stimulating factors (G-CSF). These induce the production of neutrophils that cause hyperleukocytosis.