Increasing attention has been focused on the implications of obesity in adults on the development of kidney disease, but data on the obese pediatric population are lacking. The aim of this study was to investigate whether changes in various renal function indexes/markers, as expressed by the glomerular filtration rate [GFR, as estimated by the Schwartz formula (eGFR)], serum cystatin C (CysC) level, albumin excretion rate (AER), and modifications in nitric oxide (NO; an important modulator of renal function and morphology), urinary isoprostanes (markers of oxidative stress), and blood pressure (BP), can be detected in obese children and adolescents when compared to normal weight controls. Blood and urinary samples were collected to evaluate markers of renal function, serum and urinary NO, and urinary isoprostanes in 107 obese Caucasian subjects and 50 controls. Ambulatory BP monitoring (ABPM) was performed in all cases. Obesity was expressed by the body mass index standard deviation score (SDS-BMI), and insulin resistance by the homeostasis model assessment of insulin resistance (HOMA-IR). CysC and eGFR did not significantly differ between the two groups; AER was increased in obese children. CysC and GFR were related to HOMA-IR, and AER was related to HOMA-IR and SDS-BMI. Obese subjects had reduced NO levels and increased urinary isoprostanes and BP measurements; all three parameters were related to SDS-BMI and insulin resistance. ABPM showed an increased incidence of hypertension and non-dipping in the obese group. Based on our comparison of obese and nonobese children, we conclude that renal involvement is not an early clinically evident manifestation of adiposity in childhood, since no overt changes in eGFR and only a mild albuminuria were detected. A longer exposure to obesity is probably needed before renal function impairment appears.