The results in morbidity and mortality between 415 newborn infants with birth weight under 2,500 g are presented; the patients with great congenital malformations were not included. The population was divided in three categories 1,500-2,499 g, 1,000-1,499 g and less than 1,000 g and each categorie was divided in small for gestational age (SGE) and appropriate for gestational age (AGE). The mortality rate was very high in the extreme low birth weight. 67% of the population were AGE y 33% for SGE. The intrahospitalary morbidity was different between each group, being the SGE with less morbidity and less length of hospitalization, with no relation to birth weight. In our study there was no differences between perinatal asphyxia and birth weight, probably because the SGE babies born in better conditions than the other group.