OBJECTIVE To determine whether blood pressure at baseline was associated with incidence or progression of diabetic retinopathy during a 10-year interval in a population-based cohort. METHODS A probability sample of all persons receiving primary care for diabetes in an 11-county area of southern Wisconsin were invited to participate in the study examinations in 1980 to 1982, 1984 to 1986, and 1990 to 1992. METHODS Blood pressure measurements, height, weight, ocular photographs, and glycosylated hemoglobin measurements were obtained and ocular examinations and a medical history interview were performed at each evaluation. METHODS Fundus photographs of seven standard photographic fields were obtained and graded according to the modified Airlie House Classification scheme. End points were incidence, any progression, or progression to proliferative diabetic retinopathy. RESULTS At the baseline examination, 996 subjects were determined to have younger-onset diabetes and 1370 subjects had older-onset diabetes compared with 891 and 987, respectively, at the 4-year follow-up examination and 765 and 533, respectively, at the 10-year follow-up examination. In discrete linear logistic analyses, a 10-mm Hg increase in systolic blood pressure was significantly associated with incidence of retinopathy in subjects with younger-onset diabetes 10 years after the baseline examination (odds ratio, 1.27; 95% confidence interval, 1.03 to 1.57). No consistent association of blood pressure and retinopathy in subjects with older-onset diabetes was observed. Mortality did not affect the relationship of blood pressure and retinopathy. CONCLUSIONS Increased systolic blood pressure at baseline was associated with a modest subsequent increased risk of incidence of diabetic retinopathy in subjects with younger-onset diabetes.