Balloon dilatation of valvar and vascular stenoses has become routine therapy in pediatric cardiology. Repeated balloon inflations cause many episodes of low cerebral oxygen delivery. This study is a prospective study to assess the effects of balloon dilatation on cerebral perfusion and oxygenation. The study included 11 patients scheduled for elective catheterization and balloon dilatation at a university pediatric hospital. Blood flow velocity in the middle cerebral artery (Vmca) and regional cerebral oxygen saturation (rSO2) were monitored by means of transcranial Doppler sonography and near infrared spectroscopy, respectively. In group 1, consisting of 6 patients without an intracardiac shunt, inflation of the balloon resulted in a decrease in Vmca followed by a minor decrease in rSO2. In group 2, consisting of 5 patients with an interatrial communication, inflation resulted in an increase in right-to-left shunt fraction, arterial desaturation. and a major decrease in rSO2 with minor changes in Vmca. Balloon dilatation causes an important decrease in cerebral oxygen delivery by different mechanisms. This may lead to serious morbidity and even mortality. Neuromonitoring is a useful tool in assessing the cerebral effects of balloon dilatation and brain recovery.