OBJECTIVE: To evaluate the reliability and validity of the Brazilian version of the Echelle Douleur Inconfort Nouveau-Ne, which measures prolonged pain in neonates. METHOD: A methodological study carried out with 96 neonates. The Brazilian versions of the Echelle Douleur Inconfort Nouveau-Ne and the Children’s and Infants’ Postoperative Pain Scale were used for data collection. For reliability, equivalence measured by intraobserver agreement and homogeneity were considered. To evaluate the validity, the convergent construct approach was considered correlating the Brazilian versions of the Echelle Douleur Inconfort Nouveau-Ne and the Children’s and Infants’ Postoperative Pain Scale. RESULTS: In assessing reliability, the coefficient of agreement between observers varied between 0.64 and 0.85 for the items that make up the instrument, and 0.96 for the total score. Cronbach’s alpha was 0.82. Regarding the convergent validity evaluation, Spearman correlation coefficient between the values found for both scales was 0.79 (p< 0.0001). CONCLUSION: The Brazilian version of the Echelle Douleur Inconfort Nouveau-Ne is a reliable and valid instrument for assessing prolonged pain in neonates.