Retinas of 142 eyes from 71 premature infants on whom autopsies had been done were studied by gross observation and by using PAS-stained whole mount, trypsin-digest, and conventional histological techniques. With these techniques, vascular pathologic condition was correlated with fluorescein angiograms in living infants with acute retrolental fibroplasia. The specific lesions seen in acute phase were a major arteriovenous shunt in the eye, microvascular changes including tufting, and obliteration of capillaries around arteries and veins. Regression occurred by vascular budding from the anterior edge of the shunt. Observations on vascularization in the normal indicated a variability of the level of maturation of the retinal vasculature, only roughly correlated with gestational age.