Keywords:Phenylephrine, hydrocephalus, preterm, mydriatic drops AbstractAdequate pupil dilation is needed to evaluate some neonates at risk of developing illness during this stage. However, this procedure is not free of adverse effects, either local or systemic. One of these complications is the local vasoconstriction of the preterm baby's skin following the application of mydriatic eye drops. Objective: To describe secondary local and systemic complications of pharmacological pupil dilation in 2 newborns. Clinical case 1: Full term baby with diagnosis of low-birth weight and hydrocephalia. An ophtalmological evaluation was performed at 5 days of age due to the presence of corneal opacities. Peri ocular pallor was observed during the procedure, as well as tachycardia and hypertension 2 hours later, spontaneosly recovered. Case 2: Preterm newborn, 27 weeks of gestational age. Neonatal respiratory distress syndrome, patent ductus arteriosus, intraventricular hemorrhage and hydrocephalia were diagnosed at birth. At 28 days of life an ophtalmological evaluation was performed. After 10 minutes of mydriatic drops administration to evaluate preterm retinopathy, peri ocular pallor was observed, with spontaneous resolution; however, 24 hours later, the patient showed abdominal distention and feeding intolerance. Necrotizing enterocolitis was discarded, and symptoms were spontaneosly recovered. Conclusion: The establishment of protocols in relation to the number of drops to apply for dilation is needed to reduce deleterious effects on high risk infants, such as premature babies and those with hydrocephalus. Therefore this monitoring practice should be performed during the evaluation.clinical caSe