Pseudoaneurysm of the right ventricle outflow tract (RVOT) is a rare complication in pediatric cardiac surgery. We report a patient who developed a right ventricular pseudoaneurysm 8 months after RVOT enlargement using a pericardial patch for infundibular pulmonary stenosis. Our patient was born with severe pulmonary valvular stenosis and treated with percutaneous balloon valvotomy in the neonatal period. Six months later, she developed infundibular pulmonary stenosis, which required surgical resection of right ventricle infundibular trabeculations and bovine pericardial patch enlargement. The postoperative period was normal. She was readmitted to hospital 5 months later complaining of wheezing, coughing and shortness of breath. Echocardiography showed a huge aneurysmal dilatation of the outflow patch in connection with the right ventricular cavity. The patient underwent resection of the pseudoaneurysm and former patch, followed by interposition of a bovine jugular vein conduit between the RVOT and pulmonary bifurcation. The early postoperative period was uncomplicated. On echocardiography, no significant residual gradient was measured through the conduit and there was no insufficiency of the valve. RVOT reconstruction with patch enlargement, homograft or conduit implantation can be the origin of pseudoaneurysms. Although their incidence is rare, they are often asymptomatic before becoming quite large and causing compression symptoms as in our patient with respiratory complaints due to airway compression. It is important to follow up these patients closely, especially in the first year after surgery since most aneurysms develop within 6 months of surgery.