Magnetic resonance imaging demonstrated coexistent central nervous system abnormalities in 30 of 40 patients with optic nerve hypoplasia. Based on their associated neuroradiological findings, these patients were placed into one of five categories: group 1, isolated optic nerve hypoplasia; group 2, absence of the septum pellucidum; group 3, posterior pituitary ectopia; group 4, hemispheric migration anomalies; and group 5, intrauterine/perinatal hemispheric injury. Posterior pituitary ectopia (group 3) and cerebral hemispheric abnormalities (groups 4 and 5) were found to be highly predictive of pituitary hormone deficiency and neurodevelopmental deficits, respectively. Isolated absence of the septum pellucidum (group 2) was associated with normal neurodevelopmental and endocrinologic function. Thinning or agenesis of the corpus callosum was predictive of neurodevelopmental problems only by virtue of its frequent association with cerebral hemispheric abnormalities. Magnetic resonance imaging can now be used to provide specific prognostic information regarding the likelihood of neurodevelopmental deficits and pituitary hormone deficiency in infants with optic nerve hypoplasia. The prevailing notion of septo-optic dysplasia as a distinct nosologic entity should be reconsidered.