Normal aortic root dimensions are established using 334 sequential echocardiograms in 111 average-gestational-age premature infants between 600-2500 g. The aortic roots increased in diameter from 0.53 cm +/- 0.04 cm for infants weighing 600-900 g to 0.80 +/- 0.08 cm for infants weighing between 2200-2500 g.