Sixty-six patients with insulin-dependent diabetes mellitus (IDDM) initiated insulin pump treatment under routine conditions. Four patients (6%) discontinued treatment. One patient died. 61 patients were followed for a total period of 130 patient years. A sustained decrease in HbA1c was obtained during insulin pump treatment. The frequency of the following acute side effects was: ketoacidosis 0.06 episodes per patient per year, severe hypoglycaemia 0.09 episodes per patient per year and infection at the injection site 0.06 episodes per patient per year. Insulin pump treatment was well accepted by the patients; all but one wanted to continue insulin pump treatment. The major advantages were greater quality of life, greater flexibility as to meal times and better blood glucose regulation. The major disadvantages were technical problems: blockage of the infusion system, greater treatment expenses and the large pump size. We conclude that insulin pump treatment is well accepted as long-term treatment in selected IDDM patients. The improvement in metabolic control can be sustained through several years, and the frequency of severe hypoglycaemia during pump treatment is comparable to that of conventional insulin treatment. The risk of ketoacidosis requires more attention from the physician.