To establish an integrated non-invasive method for diagnosing coarctation, cross-sectional echocardiographic appearances of 48 neonates and infants with coarctation were combined with clinical information on the peripheral pulses. Measurements of the ascending aorta, aortic arch, and isthmus were made and compared with those from controls matched for weight and age. Confirmation of the coarctation was available in all cases. Angiocardiographic measurements were performed in 15 patients from either the group with coarctation or the controls. After the aortic arch had been analysed segment by segment 40 patients were found to have preductal coarctation, five juxtaductal coarctation, and three postductal coarctation. In one of the patients in the latter group the obstruction was situated in the abdominal aorta. Specific echocardiographic features were present in each subgroup. Echocardiographic measurements were about two thirds of those obtained by angiocardiography. By combining information on the peripheral pulses, isthmic size, and the presence of a discrete shelf in the aorta it was retrospectively possible to predict correctly the presence of coarctation in 45 out of 48 cases. Since the beginning of this study 29 patients have undergone surgery without prior invasive investigation. A combination of clinical assessment and cross-sectional echocardiographic features allows a reliable diagnosis of coarctation to be made in most cases.