Cranial ultrasonography is an essential examination for newborns and infants. Its use avoids exposure to radiation and the need to sedate the patient. Further, ultrasonography can be used repeatedly at the bedside and with good resolution. We use a sector probe because the narrow anterior fontanella serves as the echo window. Echo images obtained from newborns and infants are very clear. We establish four basal sections in the saggital and coronal regions to maintain the objectivity of the images. The major advantage of cranial ultrasonography derives from its ability to visualize shape using B mode. Ultrasonography is the method of choice in diagnosing cranial hemorrhage, periventricular leukomalacia, infections (congenital cytomegalovirus infection, encephalitis and meningitis), malformation (Dandy-Walker syndrome, and agenesis of the corpus callosum). The pathophysiology of newborn asphyxia, cranial hemorrhage, and hydrocephalus can be estimated from cranial blood flow. Three dimensional ultrasonography is a new technology now being used to examine various organs. It enables us to measure the volumes of the lateral ventricles and grasp the shape of objects in three dimensions. Although, histologic diagnosis using ultrasonography remains difficult, RF signal analysis may make it possible.