A follow-up study of 116 Type 1 (insulin-dependent) diabetic patients on long-term continuous subcutaneous insulin infusion was conducted after 4.5 +/- 0.2 years. The average HbA1c-value of these patients decreased by 1% to 6.7 +/- 0.1% during this observation period. Typical side effects of continuous subcutaneous insulin infusion such as skin inflammation at the catheter insertion site occurred with similar frequency as has been reported previously by other authors. Diabetic ketoacidosis (0.14 per patient year) and disabling hypoglycaemia (0.1 per patient year, including 0.05 hypoglycaemic coma per patient-year) occurred at substantially lower rates than in other comparable studies with Type 1 diabetic patients at a similar degree of metabolic control. Subgroup evaluation suggested that a normal (less than 5.6%) HbA1c-value at follow-up was associated with increased incidence of disabling hypoglycaemia, whereas poor metabolic control (HbA1c greater than 7.5%) was associated with increased rates of skin complications and hospital treatment for ketoacidosis. Thus, under the policies of this diabetes centre, continuous subcutaneous insulin infusion has proved to be beneficial to a large proportion of experienced adult Type 1 diabetic patients, who voluntarily had opted for, and continued with, this particular mode of insulin treatment.