A progressive retinal atrophy (PRA) affecting Miniature Schnauzer dogs is reported. Of the 287 individuals (148 female, 139 male) comprising the study population, 66 (23 percent) were affected (33 female, 33 male) and 221 animals (115 female, 106 male) were phenotypically normal. There was no sex predilection for the disease. Results of histologic and electroretinographic studies indicate that the disease is a new and different type of PRA, characterized by unique morphologic and functional deficits during rod and cone development. Accordingly, the disease has been termed photoreceptor dysplasia. Clinically, and particularly ophthalmoscopically, diagnosis is only practicable in very late stages of the disease. Electroretinography, however, can provide evidence of the disease in dogs at least as young as 8 weeks of age. Pedigree analysis and test-mating studies conclusively establish that inheritance is autosomal recessive. The gene symbol pd (for photoreceptor dysplasia) is assigned.