Neonatal septicemia was assessed by blood cultures in 115 newborns (NB) during a two years study in a pediatric hospital of reference in Mexico City. The studied patients were divided in two groups of gestational age, and the differences of etiologic agents, clinical signs, laboratory findings and clinical outcome were compared at term and preterm neonates. We observed Staphylococcus epidermidis became the first cause of septicemia in at term NB (P less than 0.001), while Escherichia coli and Klebsiella pneumoniae (P less than 0.01) were more frequent in the preterm neonates. The clinical manifestations of fever (P less than 0.001), hepatomegaly (P less than 0.01), splenomegaly (P less than 0.05), and rejection to feeding (P less than 0.05) were more common in at term NB. On the other hand, apneas (P less than 0.01), hypothermia (P less than 0.02), and abdominal distension (P less than 0.05) were more frequent in the preterm NB. The altered white blood cell counts were more commonly observed in the preterm group, as leukopenia (P less than 0.05), neutropenia (P less than 0.01), and high I/T ratio (P less than 0.05). There were not significant differences in complications or sequels between the two groups; however, the mortality ratio was higher in the preterm NB group (P less than 0.02). Changing etiology of neonatal septicemia is discussed, and we propose these kind of data are very useful for purpose of detection, diagnostic and treatment of septic neonates.