Background: Obesity during childhood is a risk factor for developing cardiovascular diseases during adulthood. Aim: To measure insulin and glucose levels and parameters of insulin resistance in obese, overweight and normal weight Mexican children. Material and Methods: Comparative study of 21 obese children with a body mass index (BMI) over percentile 95, aged 10 1 years (10 males), 14 children aged 10 2 (7 males) with a BMI between percentiles 85 and 94 and 16 children aged 9 2 years (3 males) with a body mass index between percentiles 10 and 84. Body weight, blood pressure and waist circumference were measured and a blood sample was obtained to measure fasting glucose and insulin levels. Homeostasis model of insulin resistance (HOMA) and quantitative insulin sensitivity check index (QUICKI) were calculated. Results: Among obese, overweight and normal weight children, insulin levels were 14.9 (95% CI 10.90-18.99), 7.20 (CI 5.12-9.28) and 4.73 (CI 95% 1.92-7.53) uU/ml, respectively. The figures for HOMA were 3.16 (95% CI 2.20-4.12), 1.49 (95% CI 1.03-1.94) and 0.97 (95% CI 0.35-1.60), respectively. The figures for QUICK' were 0.331 (95% CI 0.319-0.343), 0.371 (95% CI 0.349-0.393) and 0.419 (95% CI 0.391-0.446), respectively. Compared to their normal weight counterparts, the risk of obese children and those with a waist circumference over percentile 90 of having a HOMA over 3.16 was 17 and 10 times higher, respectively. BMI correlated better than waist circumference with insulin levels. Conclusions: Obese children have higher levels of insulin resistance than their normal weight counterparts.