The aorta, right pulmonary artery and pulmonary trunk were measured from the 2-dimensional echocardiogram (2-D echo) of 110 normal subjects aged 1 day to 18 years. The vessel diameters were measured from the parasternal short-axis view, the suprasternal long-axis view and the suprasternal short-axis view. Measurements were made at end-systole and at end-diastole and in both an axial and lateral direction where possible. When analyzed with respect to body surface area (BSA), the echocardiographic measurements were linearly related to the square root of the BSA, and there was inequality of variance around the relation. To establish a range of normal values for each vessel dimension, a weighted regression analysis was used to produce estimates of the regression line and a set of tolerance intervals. The systolic vessel dimension was larger than the diastolic vessel dimension and the measurement of a vessel in an axial direction was larger than the measurement of the same vessel in a lateral direction. In general, when a vessel was measured in several views, the largest diameter was obtained using the view that imaged the vessel in cross section. These data on normal values for the echocardiographic measurement of the aorta and pulmonary arteries at different BSAs should be useful for identifying patients with abnormalities in arterial size and for the serial assessment of arterial size in children who have undergone surgical or medical therapy.