Two children were seen with paracardiac masses, whose nature was determined by two-dimensional (2-D) echocardiography. The information gained as to the relation of these masses to the heart is presented. The first child had a large cystic mass located posterior to and partially compressing the left atrium and ventricle. The second child had a large mass with central necrosis compressing but not communicating with the right atrium. Thus, 2-D echocardiography is a noninvasive and generally available technique which can provide the same or more information in the diagnosis of mediastinal and paracardiac masses as cardiac angiography and CT scanning without carrying the hazard of radiation to small children.