Three stages of macular degeneration associated with diffuse cone-rod dystrophy have been described in a Guinea baboon (P papio) colony. Clinically, the affected animals displayed abnormal behavior associated with decreased vision. Ophthalmoscopically, the lesion in the macula was the only change observable in early cases; retinal vessel attenuation and optic disc pallor were seen only in the advanced cases. The hyperfluorescence of the maculae was the result of loss of pigment in the pigmented epithelium. Electrophysiology supported a cone-rod sequence of this retinal dystrophy. Histologic examination confirmed the theory that the dystrophy began in the cone outer segment but eventually involved all the photoreceptors.