The mediastinum is a common site for germ cell tumors. We describe an
unusual case in an 18-month-old girl who presented with respiratory di
stress and cardiomegaly. An echocardiogram revealed a large pericardia
l effusion and a mass adjacent to the heart. She underwent detailed in
vestigation and at open exploration was found to have a wholly intrape
ricardial malignant yolk sac tumor. Staging investigations revealed a
bony metastasis. The serum marker alpha-fetoprotein was elevated. She
was treated with chemotherapy and is in remission 1 year after complet
ion of treatment. We review the methods of diagnosis and follow-up of
children with these tumors.