Objective: This paper aims to analyze the use of off label (OL) medicines, according to the National Regulatory Agency, in a neonatal intensive care unit of a high-risk maternity hospital in Northeast Brazil. Methods: A cross-sectional study was carried out, using a convenience sample of newborns that used mechanical ventilation at the Intensive Care Unit. As a reference, OL medications were considered for those without an approval for newborn usage by the Brazilian Health Regulatory Agency (Agência Nacional de Vigilância Sanitária - ANVISA) and by the Food and Drugs Administration (FDA). Results: The sample consisted of 158 newborns, 58.3% male, 87.7% premature, and 70.2% of low or very low birth weight. According to ANVISA, 440 out of the 1,167 prescriptions analyzed were OL, with 98.1% of newborns exposed to at least one of these drugs. According to the FDA, 484 prescriptions were OL, with 75.8% of newborns exposed to at least one of them. Anti-infectives were the most prescribed OL medications. Neonates who presented respiratory failure and pneumonia used these drugs more often; and there was no relation between their use and the number of deaths. Conclusions: Nearly all newborns at the Intensive Care Units, mainly preterm infants, are exposed to at least one off-label (OL) medication during hospital stay, according to the national and international regulatory agencies. No association was found between off-label prescriptions and the frequency of complications or neonatal deaths.