Objectives Endothelial dysfunction is a known precursor of atherosclerosis and can be assessed by measuring the brachial artery flow-mediated dilatation (FMD) via ultrasonography. This study investigated endothelial function in young type 1 diabetics without cardiovascular morbidity or diabetes-related pathology. Methods Young diabetics and healthy controls were recruited, both meeting strict inclusion and exclusion criteria. To prove absence of subclinical atherosclerosis, intima-media thickness (IMT) measurements at the carotid bifurcation were done in all of them. FMD was measured at the brachial artery. The results were compared using the t-test and the influences of different variables on FMD were assessed using multiple linear regression. Results Twenty-six diabetics (23.4 ¡À 5.8 years) and 36 healthy volunteers (23.1 ¡À 2.8 years) were recruited. The duration of diabetes was 9.2 ¡À 5.3 years; metabolic control was moderate (HbA1c 7.6 ¡À 1.0%) and IMT was normal in both groups. FMD was significantly impaired in type 1 diabetics (7.13 ¡À 0.43 vs. 8.77 ¡À 0.43%; p = 0.002). The FMD grade was associated with diabetes and age. Patients with a good metabolic control (HbA1c ¡Ü 7.0%) had a better FMD. Conclusions In type 1 diabetics, even without preclinical or clinical atherosclerosis, endothelial function is already disturbed and can be detected using ultrasonography.