The aim of this study was to validate a definition to identify cases of early neonatal near miss using data from health information systems (SIS in Portuguese). This was a concurrent validation study focusing on three definitions for identification of cases of early neonatal near miss among live births in a university hospital in 2012. Three different definitions were applied to this live birth cohort using the criteria birth weight, gestational age, 5-minute Apgar score, admission to the neonatal intensive care unit, mechanical ventilation, and congenital malformations, in different combinations, considering the proposals in two Brazilian articles (Silva et al.; Pillegi-Castro et al.) and a third (SIS definition) with available data from health information systems. Cases were defined as infants that had survived the risk conditions as of the 7th day of life. For concurrent validation, the study adopted early neonatal deaths as the reference. Of the 2,097 live births studied, 33 died in the early neonatal period, and the number of cases of early neonatal near miss varied according to the definition used: 153 (Silva definition), 194 (Pileggi-Castro definition), and 304 (SIS definition). Sensitivity and specificity were 97% and 92.6%, respectively, according to the Silva definition, 90.9% and 90.6% according to the Pileggi-Castro definition, and 93.9% and 85.3% according to the SIS definition. The results show that the SIS definition has sensitivity and specificity close to the other definitions and suggest that it is possible to monitor early neonatal near miss using only data that are available in official health information systems.