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OBJECTIVE—The aim of the present study was to evaluate serum and urinary nitric oxide (NO) concentrations in children and adolescents with diabetes compared with age-matched healthy control subjects to find out whether Doppler ultrasonography could be used to detect changes in renal resistive indexes (RIs) in children with diabetes and to assess whether there are correlations between these parameters and NO excretion. RESEARCH DESIGN AND METHODS—We studied 42 children with type 1 diabetes and 41 matched healthy control subjects, both divided into prepubertal or pubertal children. Serum and urinary nitrite and nitrate (NO2−+NO3−) concentrations were evaluated as an index of NO production. Doppler ultrasonographic registration of intrarenal RI was performed. RESULTS—Compared with healthy control subjects, children with diabetes had significantly increased concentrations of serum (30.26 ± 6.52 vs. 24.47 ± 7.27 mmol/l, P = 0.001) and urinary NO2−+NO3− (345.07 ± 151.35 vs. 245.86 ± 80.25 mmol/l, P = 0.002); the same was true for Doppler RI values (0.64 ± 0.03 vs. 0.60 ± 0.04, P = 0.035). This occurs in both prepubertal and the pubertal children. A significant positive correlation was found between serum and urinary NO2−+NO3− levels (P = 0.002, r = 0.374). Serum NO2−+NO3− concentrations also correlated positively with Doppler RI (P = 0.032, r = 0.262) and HbA1c (A1C) (P = 0.004, r = 0.329); urinary NO2−+NO3− concentrations correlated positively with A1C (P = 0.001, r = 0.394). Doppler RI correlated positively with A1C (P = 0.000, r = 0.424). CONCLUSIONS—This study demonstrates that in children with diabetes, chronic hyperglycemia may act through a mechanism that involves increased NO production and/or action and contributes to generating intrarenal hemodynamic abnormalities, which are detectable by Doppler ultrasonography even in early diabetic nephropathy.