Vitamin D deficiency is known to be common in patients with type 1 diabetes. Studies in adults have shown that vitamin D deficiency is associated with cardiovascular events such as stroke, myocardial infarction and peripheral arterial disease. However, the impact of this deficiency on vascular health in adolescents with diabetes has not been examined. Furthermore given that endothelial dysfunction is reversible, early detection of this process may have therapeutic and prognostic implications in this population.