To determine the influence of pregnancy on the retinas of insulin-dependent diabetics, we assessed 53 diabetic women by retinal photography every six weeks throughout pregnancy and for six months post partum. Thirty-nine nonpregnant insulin-dependent diabetics of childbearing age served as controls. Of the 39 controls, 18 (46.2%) had retinopathy. Of the 53 pregnant women, 33 (62%) had retinopathy at the first examination and eight others (15%) developed it as pregnancy advanced, significantly increasing the prevalence of retinopathy during pregnancy to 77.4%. Progressive changes occurred as pregnancy advanced; microaneurysms moderately increased, hemorrhages appeared in 30 (56.6%), and soft exudates in 15 (28.3%). Four patients (7.5%) had neovascularization, one for the first time. The condition of all four deteriorated during pregnancy. Six months after delivery the background changes had regressed to control levels. Neovascularization showed some regression. Duration of disease was related to the development and progression of retinopathy; every pregnant patient who had had diabetes for ten years had retinopathy. Retinal hemorrhages or neovascularization were associated with increased infant morbidity. Hemorrhages and exudates behaved independently and were associated with different risk factors, but increased insulin requirements and polyhydramnios were important risk factors in the development of retinal hemorrhages. Low fasting blood glucose levels late in pregnancy were significantly associated with soft exudates.