The aim of this study was to evaluate the prevalence of chronic complications in patients with type 1 diabetes with more than 30 years of history of the disease, depending on the age of onset of diabetes. The criterion for inclusion in the study was over 30-year history of type 1 diabetes. The study group was divided into two subgroups according to the age of diagnosis of type 1 diabetes (either before or after 18 years of age). Anthropometric parameters, degree of metabolic control and the presence of markers of chronic diabetic micro- and macrovascular complications were assessed. The study was performed in 215 type 1 diabetic patients with more than 30 years history of the disease, aged 54±10 years, 98 men, 117 women. In 110 patients (group I), type 1 diabetes was diagnosed before age of 18 years, in 105 patients (group II) after 18 years of age. Patients in group I were younger, with a longer duration of the disease, more often treated with intensive functional insulin. There were no differences in terms of metabolic control between the assessed groups. Patients in group I were significantly more often diagnosed with chronic diabetic kidney disease, in group II hypertension was more often observed. Conclusions. The diagnosis of type 1 diabetes before or after the age of 18 had no significant effect on the lack of chronic complications. Patients with diabetes diagnosed in childhood, after 30 years of disease, presented a higher incidence of diabetic kidney disease.