In a group of 69 insulin dependent diabetics aged 19-59 years (mean 25.5 years) with a duration of diabetes of 2 to 34 years (mean 12.5) the authors assessed the incidence of diabetic retinopathy, nephropathy and neuropathy in relation to the duration of diabetes, to its long-term compensation and HLA antigens. In 45 the diabetes was manifested before the age of 15 years. The authors found a rising trend of retinopathy (12-14-25-75-86%) and neuropathy (0-50-60-85-83%) in five groups with a duration of diabetes up to 5, 10, 15, 20 and above 20 years. 15% of the patients with a duration of diabetes of more than 15 years had positive microalbuminuria or permanent proteinuria and hypertension. In diabetic patients with long-term satisfactory compensation there was a lower incidence of these complications than in patients with poorer compensation. The presence of HLA B8 antigen was associated with a prolonged favourable course of diabetes, with a lower incidence and later manifestation of complications.