Ultrastructural study of Norrie's disease. We studied the clinicopathologic and ultrastructural features of a full-term infant with Norrie's disease. The infant had bilateral retrolental fibrous vascular masses and retinal detachment with no other apparent physical abnormalities and no family history of ocular defects. A vitrectomy and a membrane peeling were attempted, and specimens of the retina, the retrolental membrane, and a vascularized epiretinal peripheral mass were examined by light and electron microscopy. The retrolental membrane was composed of layered collagenous tissue and contained structures resembling blood vessels. Inner and outer neuroblastic layers were identified in the retinal tissue, but no vessels were present. In the epiretinal mass, portions of retina and cortical vitreous were seen along with primitive vascular structures. The histologic appearance of these specimens suggests that the major pathologic event of Norrie's disease occurs in the retina in the third to fourth gestational month. We believe the subsequent ocular abnormalities found in this patient were secondary to this early retinal malformation and did not represent a progressive ocular disorder. 