In intensive insulin therapy frequent measurements of blood glucose are necessary for daily insulin adjustments. The aim of our study was to determine acceptance of frequent blood glucose measurements and its relation to quality of glycemic control over a period of 5 years. We report on 57 unselected patients with type 1 diabetes mellitus, who were at least half a year under intensive insulin therapy when entering the study. Mean age was 34 +/- 9, diabetes duration 18 +/- 8 years. The number of daily blood glucose measurements, HbA1c, body mass index, daily insulin dose, routine laboratory values, number of severe hypoglycemic reactions and frequency of retinopathy, nephropathy and neuropathy were determined for year 1 and 5. We found an increase in daily blood glucose measurements from 2.5 to 4.5 per day (year 1 resp. year 5). The frequency of blood glucose measurements at the begin of our study respectively after 5 years was: < or = 2.0/day in 51% vs. 12%, > 2.0 but < 4.0/day in 20% vs. 21% and > or = 4.0/day in 29% vs. 67% of patients. HbA1c decreased from 7.3 +/- 1.2 to 6.4 +/- 1.1% after 5 years (p < 0.001). A comparison of subgroups of patients showed that frequency of blood glucose measurement is not the only cause for this improvement, but adequate education of diabetic patients seems to be most important. Retinopathy and neuropathy increased despite better diabetic control, 2 patients developed microalbuminuria, all other data determined at study entry remained unchanged after 5 years. We conclude that frequent daily blood glucose measurements were accepted by the majority of our patients over a long period of time. Mean blood glucose determined by HbA1c improved under intensive insulin therapy. In our study group with low HbA1c values at baseline this effect was only partly related to the frequency of daily blood glucose measurements.