Although physical activity is frequently recommended in the management of type Idiabetes it has not yet been established whether practising regular exercise could actually improve the long-term outcome of metabolic control. In this follow-up study we assessed the impact of long-term physical activity in patients with type 1 diabetes mellitus. We studied longitudinally 69 patients with type 1 diabetes mellitus, 43 boys and 26 girls aged at onset of the disease 8.98 +/- 3.90 years with a mean duration of the disease of 97 +/- 63 months. The patients were classified according to the duration of the disease in 3 groups [A:24-60 months (69); B: 61-120 months (41); C > or =121 months (19)]. The average time spent weekly doing exercise was recorded for each patient in the three duration periods taken into account. On average our patients reported 3.0 +/- 2.9 hours of physical activity per week. On the basis of the hour/week of physical activity we divided the patients into 4 groups [G1: <2 hrs/week (46%); G2: 2-4 hrs/week (29%); G3 >4 hrs/week (22%) > or =7 hrs/week (3%)]. The duration group B showed a significant lower HbAlc and HbA1c adjusted for duration of the disease in G4 compared to G2 (p < 0.05) and G3 (p < 0.05). No differences were found for insulin requirement, weight excess, blood pressure and heart rate between active and sedentary patients. According to our results we concluded that exercise can improve the quality of metabolic control only if it is adjusted to the training level of the patient.