A prospective study was undertaken to determine the effect of pregnancy on diabetic retinopathy. Insulin-taking diabetic women were enrolled; one group was comprised of pregnant women, the other group was comprised of women who were not pregnant. Women were evaluated on referral and again in the postpartum period. The severity of diabetic retinopathy was based on grading of fundus photographs of seven standard photographic fields. The glycosylated hemoglobin, duration of diabetes, current age, diastolic blood pressure, number of past pregnancies, and current pregnancy status were evaluated as risk factors for progression of diabetic retinopathy. After adjusting for glycosylated hemoglobin, current pregnancy was significantly associated with progression (P less than 0.005, adjusted odds ratio 2.3). Diastolic blood pressure had a lesser effect on the probability of progression. The findings from this study indicate that pregnancy and level of glycemia are associated with progression of diabetic retinopathy.