The congenital malformation known as optic nerve hypoplasia (ONH) has been recognized in the past 30 years as an epidemic cause of congenital blindness. It was believed to occur either as an isolated anomaly or as a component of the syndrome of septo-optic dysplasia, which has evolved to include midline brain malformations and hypopituitarism. Evidence now suggests that ONH infrequently occurs in isolation. Most afflicted children will have hypothalamic dysfunction and/or neurodevelopmental impairment, regardless of MRI findings or severity of ONH. Adverse outcomes can often be ameliorated with early intervention. Thus, the syndrome of ONH should be suspected in all infants with signs of hypothalamic dysfunction or vision impairment.