OBJECTIVE: To assess the correlation between plasma lactate concentrations in the first 6 hours of life and early neonatal mortality. METHODS: The patients were divided in 2 groups based on the cutoff point, obtained from a receiver operating characteristic (ROC) curve, of the plasma lactate concentration that best predicted neonatal mortality during the first 3 days of life. The differences between groups and the correlations between the investigated variables and the plasma lactate concentrations measured in the first 6 hours of life were analyzed using the Chi-square, Student's t, or Mann-Whitney tests and logistic regression. RESULTS: The best cutoff point of the plasma lactate concentration as determined by the ROC curve for death during the first 3 days of life was 4.2 mmol/L. The investigated groups differed with regards to the average birth weight, which was lower in the group with serum lactate levels > 4.2 mmol/L, and the match between birth weight and gestational age, where the group with serum lactate levels > 4.2 mmol/L exhibited a higher number of newborns small for their gestational age. Seizures, intracranial hemorrhage, and death during the first 3 days of life occurred more frequently in the group with serum lactate levels > 4.2 mmol/L. CONCLUSION: In the investigated samples, the presence of plasma lactate concentrations > 4.2 mmol/L in the first 6 hours of life correlated with neonatal death during the first 3 days of life, a higher frequency of neurologic morbidity, and newborns that were small for their gestational age.