A total of 120 healthy infants, children, and teenagers were examined by cross-sectional echocardiography. Right and left atrial and ventricular dimensions and areas were measured in the parasternal, apical, and subcostal views. Dimensions of the inferior caval vein, the pulmonary artery and the aorta were obtained in the parasternal, suprasternal, and subcostal views. Reproducibility was studied in separate material consisting of 19 children with various forms of congenital heart disease examined consecutively by two different observers. Interobserver reproducibility was expressed as the 95% tolerance limit for the difference between two measurements. Good correlation with body surface area was demonstrated for all measurements, and the regression equations for the normal values of the parameters studied are given. Interobserver reproducibility was fairly good for measurements in the parasternal views, but moderate or low for measurements in the apical and the subcostal four-chamber views. Measurements in cross-sectional echocardiography are clinically useful, especially in the study of the right-sided cardiac structures that are difficult to evaluate with M-mode echocardiography, but the problems of reproducibility have to be taken into account.