Although formation of an aortic root abscess is a frequent complication of aortic valve endocarditis in adults, this complication has been rarely observed in children. In the majority of cases it has been described in children without underlying congenital heart disease. Due to the rarity of this complication, diagnosis and treatment is frequently delayed in childhood. We report a 21/2 year old girl who developed pericardial effusion in the course of pneumonia. Echocardiographic examinations, which were performed because of the pericardial effusion, revealed after 6 days the development of a cystic structure posterior to the aortic root. There was a perforation of this aortic root abscess to the left ventricular outflow tract; the aortic and mitral valves however were normal without endocarditic vegetations. Surgery was performed on the 10th day following a rapid increase in the size of the abscess. During surgery the abscess was drained and the perforation to the left ventricle was closed with direct sutures. Intraoperative transesophageal echocardiography confirmed a good surgical result. Blood cultures remained negative; in the material from the abscess however we found staphylococcus aureus. The postoperative course was uneventful. Our case demonstrates the necessity of detailed and repeated echocardiographic examinations in children with possible symptoms of bacterial endocarditis (in our case pericardial effusion) as well as the requirement of cultures of the abscess for identification of the infective organism. Intraoperative transesophageal echocardiography allows exact description of an aortic root abscess, its relation to other cardiac structures and immediate evaluation of the surgical result.