The aim of the present study was to evaluate the degree of metabolic control obtained with the use of the insulin analogue lispro compared to the previous regimen with classical regular insulin in children and adolescents with Type 1 diabetes mellitus. HbA1c, lipid metabolism, body mass index (BMI), frequency of severe hypoglycaemia, carbohydrate intake, total daily insulin requirements and its distribution during the day were analysed in 44 diabetics patients (57% males and 43% females) throughout a 3-yr period. The mean age of the patients at the beginning of the study was 15.6 +/- 2.7 yr with a mean duration of the disease of 8.01 +/- 3.4 yr. All data were evaluated for the year before the change of treatment, and 1 yr (44 patients), 2 yr (19 patients) and 3 yr (13 patients) after the change. HbA1c levels did not significantly change (6.6 +/- 1.1% with regular insulin, 6.32 +/- 1.05% in the 1st year with lispro, 6.6 +/- 1.1% in the 2nd yr with lispro, 6.33 +/- 0.9% in the 3rd yr with lispro). However, significant differences (p = 0.03) were found after 3 yr of treatment in those patients who changed to insulin lispro therapy due to a bad glycaemic control. The total daily insulin dose (U/kg/d) remained unchanged. The total short-acting/intermediate-acting insulin ratio significantly decreased (45.9 +/- 0.1% regular insulin; 37.2 +/- 0.1% 1st yr lispro (p < 0.001); 33.6 +/- 0.1% 2nd yr lispro (p < 0.05); 35.5 +/- 0.1% 3rd yr lispro (p < 0.05). BMI and lipid profile remained unchanged. The self-reported daily carbohydrate in take significantly decreased due to a reduction of snacks. Total number of episodes of severe hypoglycaemia did not change significantly. In conclusion insulin lispro treatment did not modify the daily insulin dose, but reduced the short-acting/intermediate acting insulin ratio. The metabolic control remained unchanged. The number of patients reporting severe hypoglycaemia was similar despite the treatment schedule. After this 3-yr duration trial all patients decided to continue the treatment with lispro insulin.