The prevalence of diabetic retinopathy and the associated medical risk factors, such as age at onset and duration of diabetes, metabolic control, blood pressure, albumin clearance and serum creatinine, were studied in 501 patients with type I diabetes mellitus. The prevalence of retinopathy, characterized as simplex, maculopathy, preproliferative, and proliferative, was 60.5%. Patients with retinopathy were younger at the onset of diabetes, and had a longer duration of disease. In patients with more than 10 years of diabetes, proliferative retinopathy was more frequent if onset was before they were 15 years old, despite the fact that the duration of diabetes did not differ. Patients with severe retinopathy had worse metabolic control, and were more frequently treated for hypertension. In addition, the systolic blood pressure was elevated in all groups of patients with any type of retinopathy, whereas the diastolic blood pressure was elevated only in patients with more severe forms. Patients with severe retinopathy also had higher levels of albumin clearance.