Conclusion: HOMA-IR, QUICKI, FGIR, and fasting insulin correlate strongly with Si assessed by the FSIVGTT in obese children and adolescents. Correlations between HOMA-ß%, FGIR and fasting insulin, and AIR were not as strong. Indexes derived from fasting samples are a valid tool for assessing insulin sensitivity in prepubertal and pubertal obese children