The authors analyse the data resulting from the first ophthalmological observation of 1,302 insulin dependent diabetics whose age at diagnosis is less than 30 years and who have been observed regularly by the Portuguese Diabetic Association. The prevalence of retinopathy is 41, 6%; 34.3% is non-proliferative and 7.3% is proliferative. Retinopathy is more frequent in males (P < 0.001). The prevalence of retinopathy increases with the duration of diabetes and it is equal to or greater than 80% in people who have had diabetes for 10 years or more. 'Poor' glucose control, the coexistence of other late complications and arterial hypertension increase the risk of retinopathy (P < 0.001).