Optic nerve aplasia is a rare congenital defect invariably associated with other ocular or systemic disorders. We examined a 3-year-old girl with monocular microphthalmos who had optic nerve aplasia on histopathologic examination of the eye after enucleation. Magnetic resonance imaging verified the presence of unilateral optic nerve aplasia, and demonstrated hemichiasmal hypoplasia on the affected side and bilateral optic tracts. The visually evoked cortical response revealed increased signals over the occipital cortex ipsilateral to the aplastic nerve, suggesting misdirection of axons from the temporal retina of the normal eye. The visual pathway in unilateral optic nerve aplasia may assume a primitive form of neuronal organization characterized by an increase in contralateral retinogeniculostriate projection.