Optic nerve hypoplasia is a developmental anomaly of the retina and optic nerves in which there is a reduction in the number of ganglion cells in the retina and of their centripetal fibers projecting through the optic nerve to the lateral geniculate body. The condition may be unilateral or bilateral and is frequently misdiagnosed as optic atrophy. In about 25% of cases, bilateral optic nerve hypoplasia is associated with a variety of cerebral malformations of which the commonest single disturbance is absence of the septum pellucidum (septo-optic dysplasia). Cerebral malformations and their endocrine accompaniments are also seen, though less frequently, in unilateral hypoplasia. The endocrine disturbances that may accompany optic nerve hypoplasia include growth hormone deficiency, adrenal insufficiency, hypothyroidism, and disturbances of antidiuretic hormone production. Precocious puberty and hypogonadism have also been observed. The prognosis of optic nerve hypoplasia depends upon the severity of the changes in the optic nerves and especially the degree of associated cerebral malformation. The finding of optic nerve hypoplasia should lead to thorough ophthalmologic, neurologic, and endocrinologic evaluation of the patient.