In a population study of all registered insulin-treated diabetic patients on the Swedish island of Gotland, the prevalence of diabetic retinopathy was determined with ophthalmoscopy, biomicroscopy, and color photography. Retinopathy was present in 173 of 368 patients (47%) and reached a prevalence of 100% after 30 years of diabetes. Proliferative retinopathy was found in 48 subjects (13%) and was more common in females (17%) than in males (9.4%) (P = .01). By simple logistic regression test, the prevalence of total and proliferative retinopathy was correlated with both duration and age at onset of diabetes (P less than .001). However, on multiple regression analysis only the relationship with duration was statistically significant (P less than .001); age at onset was not (P greater than .2). Age had an additional influence only on background retinopathy with hard exudates, which were more frequent in older subjects (P less than .01). Thus, age at onset of diabetes was not correlated with the prevalence of total or proliferative retinopathy.