Background: Vascular endothelial dysfunction and accelerated thickening of arterial intima contribute to increased cardiovascular morbidity in type 1 diabetes. Although vitamin C has important antioxidant functions, and increased oxidative stress is a central mechanism of vascular abnormalities in diabetes, the relationship between these two in young patients with this disease has not been yet investigated. Methods: Carotid artery intima-media thickness (cIMT) and cutaneous microvascular reactivity to endothelium-dependent (acetylcholine, ACH) and independent (sodium nitroprusside, SNP) were assessed by high-resolution ultrasound and laser Doppler with iontophoresis, respectively, in 43 patients (mean age: 17, range: 10-22 years) with type 1 diabetes (mean diabetes duration: 9, range: 3-20 years). For laser Doppler, five consecutive doses were applied to generate dose-response curve, and the measured skin perfusion was expressed as % maximal increase from baseline. Markers of systemic inflammation (C-reactive protein, fibrinogen and orosomucoid), lipids (total, LDL and HDL cholesterol) and glycosylated hemoglobin (HbA1c) were measured in EDTA plasma. Ascorbate was analyzed in meta-phosphoric acid-stabilized EDTA-plasma by high-performance liquid chromatography. Results: In univariate regression analysis, both cIMT and skin microvascular response to ACH correlated with ascorbate levels (r=-0.29; p=0.04, and r=0.43; p=0.004 respectively). The relationships between these vascular indexes and plasma ascorbate remained significant after adjustment for age, diabetes duration, body mass index, and HbA1c (r=-0.28; p=0.05, and r=0.35, p=0.01, respectively). No association was observed between plasma ascorbate and the inflammatory and lipid variables (p>0.2). Conclusion: In juvenile type 1 diabetes, lower plasma levels of vitamin C appears to predispose to more pronounced adverse changes in both microcirculation and peripheral arteries. Further studies are needed to investigate whether dietary supplementation with vitamin C could retard the development of microvasculopathy and atherosclerosis in young patients with type 1 diabetes.