All diabetic patients of the outpatient clinic of the University of Frankfurt/Main, who started intensified conventional insulin therapy (ICT) between 1980 and 1991, and who could be followed for at least one year (n = 141) were evaluated retrospectively. Fourteen patients changed from ICT to continuous subcutaneous insulin infusion (CSII). No patient changed back permanently to conventional insulin therapy. Mean glycosylated hemoglobin-levels (HbA1) decreased significantly in the first year from 9.3% to 8.5% and remained at a near normal level in the following years. HbA1-levels were found not to be associated with age, age at diagnosis, weight gain, frequency of visits to the outpatient clinic, number of consultations with the dietician as well as the frequency of attendance at special seminars for ICT. These results demonstrate that ICT lowered blood glucose levels permanently, that patients were highly compliant, and that ICT was practicable and safe for long-term treatment under routine conditions without initial hospitalization and with an acceptable expenditure of time for patients and medical staff.