['To explore a less invasive way of assessing preload in neonates than fitting catheters to measure central venous pressure (CVP). This study evaluated the relationship between inferior vena cava (IVC) measurements and gestational age (GA) or body weight (BW) in term and premature infants and the correlation between those measurements and CVP in sick infants under mechanical ventilation.', 'We studied 57 clinically stable infants, together with 14 sick infants fitted with central venous catheters to measure CVP. Subcostal transverse views were recorded at the level of the left branch of portal vein, and the minimum (DS ) and maximum (DL ) diameters of the IVC were measured. We evaluated the values of DS and DL and the S/L ratio (DS divided by DL ) in the clinically stable infants and the correlation between S/L and CVP in the sick infants with central catheters.', 'DS and DL correlated positively and strongly with both GA and BW, whereas S/L was almost independent of both GA and BW and correlated strongly with CVP.'] Does the diameter of the inferior vena cava provide a noninvasive way of calculating central venous pressure in neonates?