BACKGROUND: To evaluate whether circulating markers of endothelial dysfunction, such as intercellular adhesion molecule-1 (ICAM-1) and myeloperoxidase (MPO), are increased in youth with obesity and in those with type 1 diabetes (T1D) at similar levels, and whether their levels are associated with markers of renal function. METHODS: A total of 60 obese youth [M/F: 30/30, age: 12.5 ± 2.8 yr; body mass index (BMI) z-score: 2.26 ± 0.46], 30 with T1D (M/F: 15/15; age: 12.9 ± 2.4 yr; BMI z-score: 0.45 ± 0.77), and 30 healthy controls (M/F: 15/15, age: 12.4 ± 3.3 yr, BMI z-score: -0.25 ± 0.56) were recruited. Anthropometric measurements were assessed and a blood sample was collected to measure ICAM-1, MPO, creatinine, cystatin C and lipid levels. A 24-h urine collection was obtained for assessing albumin excretion rate (AER). RESULTS: Levels of ICAM-1 and MPO were significantly higher in obese [ICAM-1: 0.606 (0.460-1.033) µg/mL; MPO: 136.6 (69.7-220.8) ng/mL] and T1D children [ICAM-1: 0.729 (0.507-0.990) µg/mL; MPO: 139.5 (51.0-321.3) ng/mL] compared with control children [ICAM-1: 0.395 (0.272-0.596) µg/mL MPO: 41.3 (39.7-106.9) ng/mL], whereas no significant difference was found between T1D and obese children. BMI z-score was significantly associated with ICAM-1 (β = 0.21, p = 0.02) and MPO (β = 0.41, p < 0.001). A statistically significant association was also found between ICAM-1 and markers of renal function (AER: β = 0.21, p = 0.03; e-GFR: β = 0.19, p = 0.04), after adjusting for BMI. CONCLUSIONS: Obese children have increased markers of endothelial dysfunction and early signs of renal damage, similarly to children with T1D, confirming obesity to be a cardiovascular risk factor as T1D. The association between ICAM-1 with e-GFR and AER confirm the known the association between general endothelial and renal dysfunction.