To investigate the relationship between diabetic retinopathy (DR) and 24-h ambulatory blood pressure (ABP) in a cohort of normotensive, normoalbuminuric type 1 diabetic patients. This is a 6.1+/-3.3 year prospective study of 44 normotensive, normoalbuminuric type 1 diabetic patients. ABP was measured at the beginning and at the end of the study. Measurements of urinary albumin excretion rate (UAER) and direct and indirect ophthalmoscopy after mydriasis were performed at the start and end of the study and at least once a year. DR was observed in 12 patients at baseline. At the end of the study, eight of these patients had progressed to more advanced stages of retinopathy. Four patients developed retinopathy after the study began. These patients were grouped and classified as progressors. At baseline, progressors were older, had longer duration of diabetes, higher levels of UAER, and higher 24-h diastolic (P=0.03) and diurnal diastolic blood pressure (P=0.03). UAER and diastolic blood pressure (24h or day) remained significantly associated with development and progression of DR after multivariate analysis. High normal ABP was associated with the development or progression of DR in this cohort of normotensive, normoalbuminuric type 1 diabetic patients. Abnormalities in blood pressure homeostasis could indicate higher susceptibility to DR.