The complete blood count, the peripheral blood smear, the reticulocyte count and the platelet countin the pathological neonatal period are fundamental tests in the diagnosis and follow-up of some of the most frequent diseases in this phase of life, such as anemia and infections, which can sometimes cause great morbidity and mortality in the newborn. A bibliographic review of the results of the hemogram, peripheral lamina, reticulocyte count and platelet count in term and preterm neonates is carried out, describing the variations of these parameters in the anemia syndrome and sepsis of the newborn.