A 19-year-old woman with Sanfilippo's syndrome had poor vision, a flat electroretinographic pattern, and fundus changes similar to those in retinitis pigmentosa. Histology of her eyes by phase-contrast and electron microscopy showed extensive intracellular accumulation of fibrillogranular and membranous lamellar vacuoles in cornea, trabecular meshwork, iris, lens, ciliary body, and sclera. Retinal ganglion cells, retinal pigment epithelium (RPE), and optic nerve glia were similarly involved. Retinal pigment epithelial hyperplasia and hypopigmentation, intraretinal RPE migration, vascular attenuation, and marked photoreceptor loss were notable and closely resembled that occurring in inherited retinitis pigmentosa. We assume that the patient's blindness was due to photoreceptor cell loss, since the ganglion cells and optic nerve seemed to be intact. Although the cause of photoreceptor loss is unclear, the massive storage of acid mucopolysaccharide and lipofuscin within the RPE might disturb its essential metabolic functions and lead to photoreceptor degeneration.