Though A-mode ultrasound (US) had been used prior to the 1970s for diagnosis of brain abnormalities such as midline shift for subdural hematoma, masses and hydrocephalus, satisfactory B-mode images of the infant brain were initially produced in the early 1970s in Australia (Kossoff et al 1974Kossoff G. Garrett W.J. Radavanovich G. Ultrasonic atlas of normal brain of infant.Ultrasound Med Biol. 1974; 1: 259-266Abstract Full Text PDF PubMed Scopus (44) Google Scholar). By the late 1970s, B-mode cranial sonography was developing in several pediatric centers, and is now available and utilized throughout the world for evaluating the neonatal brain. Current common applications include the diagnosis and follow-up of neonates with intracranial hemorrhage, hypoxic-ischemic injury and congenital anomalies. Sonography is also utilized in the operating room for guidance of neurosurgical procedures and for the determination of resection of tumors. Doppler is being used to evaluate intracranial perfusion, to determine if a structure is vascular, to determine vascular patency and direction of flow. Transcranial Doppler is used for screening for vascular disease in sickle cell anemia patients amenable to treatment with transfusions. Intracranial vascular arteriovenous malformations can be diagnosed and followed during treatment. Doppler has been used to study changes in cerebral blood flow with intracranial hemorrhage, hypoxic-ischemic injury, and in patients on extracorporeal membrane oxygenation. Because US can be performed portably in the nursery and at the levels used is without known bioeffects, these current applications will continue into the new millennium. Evolving changes in the archiving of images that allow the transmission of digital images over telephone lines, the internet and via satellite will enable the interpretation of US examinations at remote sites. This will enable long-distance reading and consultative services to develop. Although problems may occur because the interpreting physician cannot make use of the information obtained with live, on-site, real-time scanning, standardized comprehensive examination will ensure that the necessary information is obtained. Another technical advancement now coming into clinical use is the three-dimensional (3-D) acquisition of US data. This allows the rapid acquisition of a large volume of data that can then be reviewed at a remote site or workstation in multiple planes (Fig. 1). 3-D has the potential of not only decreasing the actual scanning time, but improving long-distance, remote interpretation of the examination. An important limitation of US has been in the diagnosis of ischemia and infarction of the neonatal brain. The sensitivity for detecting such abnormalities with B-mode imaging is less than that of computerized tomography (CT) with contrast material and magnetic resonance imaging (MRI). The use of intravascular US contrast agents and tissue characterization techniques could increase the sensitivity of US in this application. Hypoxic-ischemic encephalopathy may be diagnosed on neurosonograms that demonstrate diffuse increased brain parenchymal echogenicity, convolutional effacement, and the obliteration of extra-axial and ventricular fluid spaces. However, up to 50% of neurosonograms in such cases demonstrate normal echogenicity on grey-scale images. Current color and power Doppler techniques demonstrate the presence or absence of flow only in relatively large intracranial vessels. Alterations in brain parenchymal perfusion are often not visible. The availability of intravascular US contrast agents will allow increased information about brain perfusion (Taylor et al 1998Taylor G.A. Barnewolt C.E. Dunning P.S. Excitotoxin-induced cerebral hyperemia in newborn piglets regional cerebral blood flow mapping with contrast-enhanced power Doppler US.Radiology. 1998; 208: 78-89Google Scholar). Altered perfusion, which is present in hypoxic-ischemic encephalopathy, will be more readily apparent, increasing the sensitivity of US in this clinical setting. Increased perfusion in areas of inflammation may also be demonstrated in patients with inflammatory disease. Quantitative analysis of US B-mode data has the potential to amplify the physician’s ability to detect and characterize parenchymal diseases of the brain that result in changes not currently distinguishable from the healthy appearance. Quantitative analysis techniques could also reduce the subjectivity of conventional qualitative US interpretation. A pilot study has shown promising results in this area (Barr et al 1996Barr L. McCullough J. Ball W.S. et al.Quantitative ultrasonic feature analysis of clinical infant hypoxia a pilot study.Am J Neuroradiol. 1996; 17: 1015Google Scholar). In the next millennium, pediatric neurosonography will continue to be an effective modality for evaluating the infant brain, due to its portability, universal availability and safety. Excellent gross anatomic and perfusion information is provided by presently available equipment. Current limitations in detecting alteration in brain perfusion in small vessels will be improved upon in the near future.