A series of 50 children aged between 1 month and 15 years old, with ventricular septal defects (VSD) were investigated by two-dimensional sector scanning and cineangiography. Fifty other children of the same age group with congenital heart disease without VSD were also investigated by two-dimensional echocardiography and angiography. No VSDs were diagnosed by echocardiography in children with angiographically intact inter ventricular septa. In the group with VSD, two-dimensional echo localised with precision: --36 membranous VSDs (36/36) --5 infundibular VSDs (5/6) --2 isolated muscular VSDs (2/2) --I atrioventricular canal type VAD (I/I) --3 multiple VSDs (3/5). The subcostal view was the most useful for visualising the VSD in 49 out of 50 cases. The parasternal views only showed the VSD in 23 cases, and the apical views only in II cases. The dimensions of the left heart chambers and the movement of the interatrial septum gave an indication of the volume of the left-to-right shunt. Dilatation of the left heart chambers and bowing of the interatrial septum into the right atrium in systole were observed in all cases where QP/QS greater than 2, except when there was an associated atrial septal defect. Two-dimensional echo also detected associated lesions: pulmonary stenosis (9/9), prolapse of an aortic valve cusp (4/5), atrial septal defect (2/2), stradling of the tricuspid valve (I/2). Two-dimensional echocardiographic short axis subcostal views are reliable in the detection and localisation of VSD. Nevertheless, trabecular and apical VSDs are particularly difficult to visualise and the use of pulsed Doppler coupled with two-dimensional echocardiography should enhance the sensitivity in diagnosing this type of VSD.