In 1975 a prospective longitudinal study of 63 non-pubescent children with insulin-dependent diabetes mellitus (IDDM) was started in order to study the development of retinopathy. This paper presents the results of a 5- and an 8-year follow-up examination concerning the individual development of retinopathy in the patients. At the last follow-up the mean age of the patients was 21.9 years (18-23 years) and the mean diabetes duration 13.2 years (8.1-21.2 years). In 1975 only 5% had developed retinopathy. In 1980 this incidence had risen to 63% and in 1983 to 93% (14% proliferative retinopathy and 79% background retinopathy). In most patients the retinopathy developed slowly, in some patients, however, it deteriorated severely within a few years. A slight regression in the number of microaneurysms and in the number of haemorrhages was observed in a few patients. Microaneurysms seemed in all but one case to be the first pathological element in diabetic retinopathy and developed as a rule several years before other diabetic fundus manifestations occurred. Development of retinopathy was correlated to the duration of diabetes. No correlation could be demonstrated between the progression of retinopathy and the status of regulation. Retinopathy occurred only in 5 patients (8%) before puberty.