A new mouse retinal degeneration that appears to be an excellent candidate for modeling human retinitis pigmentosa is reported. In this degeneration, called rd-3, differentiation proceeds postnatally through 2 weeks, and photoreceptor degeneration starts by 3 weeks. The rod photoreceptor loss is essentially complete by 5 weeks, whereas remnant cone cells are seen through 7 weeks. This is the only mouse homozygous retinal degeneration reported to date in which photoreceptors are initially normal. Crosses with known mouse retinal degenerations rd, Rds, nr, and pcd are negative for retinal degeneration in offspring, and linkage analysis places rd-3 on mouse chromosome 1 at 10 ± 2.5 cM distal to Akp-1. Homology mapping suggests that the homologous human locus should be on chromosome 1q.