Medical nutrition therapy is key factors in diabetes care. This paper investigates the performance of control of diabetes due to dietary habits, duration of disease and lifestyle subjects. The study was conducted with 23 patients, aged 9 -17 years with diabetes mellitus type 1. With parental consent, we collected diet history, which included (i) their eating habits, (ii) anthropometric biochemical parameters, and (iii) the general opinion about nutrition. The results pointed out the fact that the success of disease control decreases with duration of the disease. 50% of patients who have diabetes for less than 1 year, have HbA1c <6.5%, while none of those who have diabetes for 10 years have HbA1c <6.5%. Target value for this parameter is < 7%. The disease is better controlled by girls (lower HbA1c). 69% of respondents would prefer inclusion of a nutritionists in the team of those who care about their health, while 9% of them don’t find that necessary. Daily energy intake was below the recommended values (Ed6 676 kJ, recommended = 10 900 kJ). The results showed inferior results in the control of diabetes especially in patients with longer duration of disease, and male patients, so it would be preferably to include a nutritionist from the moment when the diabetes is diagnosed and to follow the patients during his control checks.