To determine the value of noninvasive assessment of right ventricular preload in neonates, a prospective unblinded study was performed. Thirty-seven neonates without heart disease (median birth weight 1390 g, range 900 to 4400) were studied at the neonatal intensive care unit, comparing directly measured central venous pressure (CVP) and two-dimensional echocardiographic measurement of the maximum and minimum diameter of the inferior vena cava and calculated vena cava index (VCI). CVP was higher in conventionally ventilated and high-frequency oscillatory ventilated neonates than in those breathing spontaneously ( p < 0.0001). VCI in high-frequency oscillatory ventilated patients was lower (5 +/- 4) than in spontaneously breathing (56 +/- 19) and conventionally ventilated (49 +/- 19) (p = 0.002) neonates. CVP and VCI were inversely correlated in spontaneously breathing (r = -0.631), but not in conventionally and high-frequency oscillatory ventilated patients. VCI does not predict CVP in ventilated premature neonates, the correlation is limited only to spontaneously breathing infants.