Up to the present there is controversy about blood-glucose self-monitoring in type 2 diabetes. In 842 insulin-treated type 2 diabetic patients (age 60.1 +/- 10.9, diabetes duration since diagnosis 12.6 +/- 7.6 years, relative HbA1c 1.83 +/- 0.39% [relative HbA1c = HbA1c/mean normal, HPLC, Diamat]) a cross-sectional study was conducted to assess blood-glucose self-monitoring and interactions with quality of diabetes care. There was a negative correlation (r = -0.17, p < 0.001) between the frequency of blood-glucose self-tests/week and HbA1c. Performing multivariate analysis the most important parameters associated with HbA1c (R-square = 0.10) were: The frequency of blood-glucose self-tests/week (c = -0.005, p < 0.001), the insulin-dosage/kg body weight (c = 0.001, p = 0.0032) and the participation in a 5-day structured treatment and teaching programme for patients with conventional insulin therapy (5-TTP, c = 0.085, p < 0.0001). Other factors investigated in the model (age, diabetes duration, number of insulin injections/day, sex) showed no associations. Performing a sub-group analysis in patients older than 60 years (n = 396) parameters associated with HbA1c (R-square = 0.16) were the participation in a 5-TTP (c = 0.09, p = 0.002) and the frequency of blood-glucose self-tests/week (c = -0.006, p = 0.0018) too. In an further subgroup analysis patients (n = 249) were investigated who have not participated in a 5-TTP. In this cohort there were no correlations and no associations between the frequency of blood-glucose self-monitoring and HbA1c. Then, an intervention was started: 33 out of the 249 patients participated in a 5-TTP. At the time of re-examination 1 year after participating in the 5-TTP, the relative HbA1c decreased from 1.84 +/- 0.38% to 1.61 +/- 0.30% (p = 0.007) and there was a strong association between the frequency of blood-glucose self-tests/week and HbA1c (c = -0.016, p = 0.0032, R-square = 0.25). Daily blood-glucose self-monitoring was statistically associated with better quality of metabolic control. Participation in a 5-TTP and regularly blood-glucose self-monitoring is mandatory for all insulin-treated patients with type 2 diabetes mellitus.