The relationship between blood pressure and the 4-year incidence and progression of diabetic retinopathy was examined in a population-based study in Wisconsin. Younger- (n = 891) and older-onset (n = 987) persons participating in baseline and follow-up examinations were included. Blood pressure was measured using the Hypertension Detection and Follow-up Program protocol. Retinopathy was determined from stereoscopic fundus photographs. In the younger-onset group, comparing the highest with the lowest quartile of systolic blood pressure, the relative risk for developing any diabetic retinopathy was 1.8 and for diastolic blood pressure it was 1.2; for progression of diabetic retinopathy, it was 1.1 and 1.3 for systolic and diastolic blood pressure, respectively. After controlling for other risk variables, systolic blood pressure remained a significant predictor of the incidence of diabetic retinopathy; diastolic blood pressure was of borderline significance in predicting progression in the younger-onset group. Blood pressure was not related to incidence or progression of retinopathy either in the older-onset group using insulin or the older-onset group not using insulin.