This was a prospective, observational study conducted in a neonatal intensive care unit to determine the incidence of adverse events. A specific trigger tool instrument was used, based on the one from Vermont-Oxford Network. A total of 218 neonates were followed and AEs were detected in 183 (84%) of them, with a rate of 2,6 AE/patient. Thermoregulation disorders (29%), disorders of glycemic control (17,1%) and nosocomial infections (13,5%) were the most frequent. Some AE were associated with birth weight (p<0.05). The accidental extubations and nosocomial infections were associated with hospital days. The incidence of AEs is high, especially among neonates with very low birth weight. Best practices regarding preventive strategies are necessary to improve quality of health care for these infants.