• We performed a histopathologic study of a heredofamilial retinal dystrophy in a colony of Guinea baboons. A bull's-eye appearance was noted in the maculas of six baboons of three generations. Histologic examination of 13 eyes from this colony showed primary degeneration of both rod and cone cells initially in the parafoveal region, which subsequently involved the photoreceptor cells of the equator and periphery of the retina. The retinal pigment epithelium and choriocapillaris showed mild changes in the early stages. This disease in baboons was compared with various human retinomaculopathies.