Prior to 1980, white matter abnormalities of the preterm newborn were known exclusively as pathological entities, but now cranial ultrasonography can image white matter abnormalities in life. Ultrasonographic white matter echodensities and echolucencies in low birthweight babies predict later handicap (especially cerebral palsy) more accurately than any other antecedent. With the increased availability of high resolution cranial ultrasonography and the improved skill in obtaining and reading cranial ultrasonograms, rapid gains can be expected in our understanding of white matter disorders. These advances are likely to be made in the diagnosis and classification of white matter disorders and in their epidemiologic and prognostic features, topics explored in this review.