Using the anterior fontanel as an acoustic window, two-dimensional/pulsed Doppler ultrasonography provides the opportunity to visualize and to insonate under an approximately zero degree angle the pericallosal, internal carotid, and basilar arteries. We studied the correlation between mean flow velocity and pulsatility index in guided pulsed Doppler waveforms obtained from these three vessels in 83 healthy term newborn infants. The mean flow velocity was derived from the area under the velocity curve, the pulsatility index was calculated by dividing the difference between the peak systolic and end diastolic flow velocities by the peak systolic flow velocity. The pulsatility index correlated very poorly with the mean flow velocity in the 3 cerebral vessels under study. In a clinical setting mean flow velocity and not the pulsatility index should be used as an indirect indicator of cerebral blood flow in infants.