Insulin resistance may favor increased urinary albumin excretion (UAE), leading progressively to chronic kidney disease (CKD). A recent study on non-alcoholic fatty liver disease (NAFLD), a condition of insulin resistance, associated this disease with the incidence of CKD in patients with type 2 diabetes. The aim of our study was to determine whether there is an association between insulin resistance and kidney function, based on estimates of UAE and creatinine clearance in children with biopsy-proven NAFLD. Kidney function was assessed in 80 patients with NAFLD and 59 individuals of normal weight matched for age and sex. Insulin resistance was measured by means of the homeostatic model assessment-insulin resistance (HOMA-IR) and limited to NAFLD patients by using the whole-body insulin sensitivity index. The HOMA-IR was found to differ significantly between the two groups (2.69 +/- 1.7 vs. 1.05 +/- 0.45; p = 0.002), while UAE (9.02 +/- 5.8 vs. 8.0 +/- 4.3 mg/24 h; p = 0.9) and creatinine clearance (78 +/- 24 vs. 80 +/- 29 mg/min; p = 0.8) did not. We found a significant but weak inverse correlation between insulin sensitivity and creatinine clearance in NAFLD patients (r (s) = -0.25;p = 0.02). No difference was observed in kidney function between NAFLD children presenting with or without metabolic syndrome, low or normal HDL-cholesterol, and different degrees of histological liver damage (grade of steatosis >or=2, necro-inflammation, and fibrosis). Patients with hypertension had increased levels of UAE (p = 0.04). A longer exposure to insulin resistance may be required to cause the increase in urinary albumin excretion and to enable the detection of the effect of the accelerated atherogenic process most likely occurring in children with fatty liver disease. Longitudinal studies are needed to rule out any causative relationship between insulin resistance and urinary albumin excretion.