Familial Exudative Vitreoretinopathy (FEVR) is a hereditary eye disorder, first reported in 1969 by Criswick and Schepens. It affects both the retina and the vitreous body, and is characterized by an abnormal vascularization of the peripheral retina. In the majority of cases, it is inherited in an autosomal dominant manner, but recently, a series of cases with an X-linked recessive and a few families with an autosomal recessive inheritance have also been reported. While linkage analysis has not been reported for the autosomal recessive form, the gene for the autosomal dominant form has been localized to the long arm of chromosome 11 (11q13 -q23). DNA linkage analysis of X-linked families has mapped the FEVR gene to Xp11.3 - p11.4. This is also a locus for Norrie disease (ND) which is a bilateral X-linked recessive disorder, characterized by ocular dysgenesis, progressive mental retardation and deafness. The cloning of the ND gene has made it possible to investigate the etiology of ND, as well as seve ral other clinically similar conditions. The ND gene product is ubiquitously expressed in tissues, including the brain, retina and cochlea, but not the liver. Mutational analysis of the ND gene identified the entire spectrum of segregating mutations in ND, as well as in some X-linked FEVR families, implying that ND and X-linked FEVR are allelic disorders. However, in some other X-linked FEVR families, no disease-causing mutations in the ND gene have been identified, indicating that X-linked FEVR is a genetically heterogeneous disorder. Although X-linked recessive disorders generally do not affect females, it has been shown that ND and X-linked FEVR can occur in female carriers, likely due to an unfavorable X-inactivation. The above studies have greatly improved our understanding of the retinal degeneration in ND and X-linked FEVR at the molecular level. The availability of an animal model should assist in developing a therapeutic approach, either to delay or to prevent these devastating disorders in the futur e.