In our preceding paper, the prevalence and development of retinopathy in 231 Type 1 diabetic children and adolescents were reported to be associated with the duration of diabetes and its age at onset. This paper analyses the relationships between the development of retinopathy and the following factors: age, sex, puberty, blood pressure, insulin dosage, HLA antigens, long-term glycaemic control, and serum cholesterol and triglycerides. All these variables were longitudinally evaluated in a cohort of 322 insulin-dependent patients aged 16.2 +/- 4.9 years with diabetes for 7.4 +/- 5.2 years, including those 231 subjects whose eyes were examined once or repeatedly by ophthalmoscopy and fluorescein angiography. Long-term glycaemic control from the onset of diabetes to the retinal examination was assessed by both an arbitrary score comprising different parameters and by mean values of glycosylated haemoglobin, and was categorised as good, fair, and poor. With life-table analysis, the overall median individual risk for developing early retinal changes (9.1 years) was found to be significantly influenced by glycaemic control. Minimal lesions developed earlier (8.0 years) with poor control, but later with fair (10.5 years) and good glycaemic control (12.5 years) (p less than 0.01). Mean HbA1 values below 10% delayed the onset of both incipient (10.8 years) and background retinopathy (16.6 years), while values above 10% advanced it (8.0 and 11.8 years respectively) (p less than 0.05 and less than 0.008). By multivariate regression and stepwise discrimination analyses, only 4 out of 14 variables were found to exert significant independent influences on the development of retinopathy: diabetes duration, long-term glycaemic control, serum triglycerides and age.(ABSTRACT TRUNCATED AT 250 WORDS)