The prevalence of retinopathy in children with insulin-dependent diabetes mellitus (IDDM) was studied in a population-based survey on 194 of the 216 subjects (89.8%) with IDDM aged 4.6 to 16.6 years living in the county of Oulu, Finland. The diagnosis of retinopathy was based on fundus photography. The median age of the children was 12.2 years and the median duration of diabetes 4.5 years (range 0.14.2 years). Retinopathy was found in 21 (10.8%) of cases. All of the changes seen were mild and did not require treatment. All the children with retinopathy were pubertal or postpubertal, and an association was found between the presence of retinopathy and the long-term diabetes control, duration of diabetes, age and albuminuria. Logistic regression analysis showed increasing duration of diabetes, puberty and elevated blood glycated haemoglobin to be the main risk factors explaining the occurrence of retinopathy. In patients aged 13-16 years retinopathy was also related to female sex and diastolic blood pressure, but in logistic regression analysis duration of diabetes and glycated haemoglobin were the best predictors.