The aim of this study was to determine the level of knowledge that nurses in the neonatal intensive care units (NICU) of a public birth center had about the use of the Neonatal Infant Pain Scale (NIPS) and to test how their scoring for NIPS changed before and after training. Thirty nurses applied the NIPS scale to newborns that were procedures considered painful. During the first and second evaluations, nurses diagnosed 30% infants as having pain and 70% infants as having an absence of pain. In the third and fourth evaluations, after the NIPS parameters had been explained, we observed an increase in the number of infants diagnosed with the presence of pain (65%). The results indicate the importance of formal training for the systemic evaluation of pain in newborns.