['Little is known about endothelial function in adolescents with type 1 diabetes, and we evaluated endothelial dysfunction, using reactive hyperaemia peripheral arterial tonometry (RH-PAT).', 'This prospective, observational, 1-year study focused on 73 adolescents with type 1 diabetes, using multiple daily injections or continuous subcutaneous insulin infusion. The subjects were assessed using RH-PAT, body mass index, blood pressure, fasting lipid profile, glycated haemoglobin, insulin requirements and hours of physical exercise per week.', 'Endothelial dysfunction was observed in 56 patients (76.7%), with lower mean RH-PAT scores (1.26\xa0±\xa00.22 versus 2.24\xa0±\xa00.48, p\xa0<\xa00.0001) and higher glycated haemoglobin values at baseline (8.27\xa0±\xa01.24% versus 7.37\xa0±\xa00.54%, p\xa0=\xa00.006) and as a mean of the whole period since diagnosis (8.25\xa0±\xa01.22% versus 7.72\xa0±\xa00.82%, p\xa0=\xa00.034). A higher percentage of patients with endothelial dysfunction showed abnormal cardiac autonomic tests (p\xa0=\xa00.02) and were more sedentary, exercising <4 hours a week, than patients with normal endothelial function. After follow-up in 64/73 patients, we observed endothelial dysfunction in 81.8% of patients, despite a modest improvement in glycated haemoglobin.'] Do adolescents and young adults with type 1 diabetes display a high prevalence of endothelial dysfunction?