Many animal models of retinal disease use the neonatal rat. Raising rat pups in large litters has been shown to result in postnatal growth retardation. We investigated the effect of litter size on the normal postnatal vascularization of the neonatal rat retina. Sixty-six newborn rat pups were divided among 5 nursing mothers into 3 small litters (n = 10) and 2 large litters (n = 18). On day 6 of life the rats were sacrificed and total retinal and vascularized retinal areas analyzed. The total retinal area was reduced in the rats raised in larger litters (28.6 mm2 vs. 25.9 mm2 p < 0.001) but there was a more pronounced reduction in vascularized retinal area (67% vascularized vs. 54% vascularized, p < 0.001). Postnatal vascularization of the normal rat retina may be influenced by litter size.