Aims of this study were i) to analyse in a large group of obese Italian children the potential relative role of the interaction of not-genetic factors such as BMI, waist circumference and insulin resistance in exposing the association between the I148M polymorphism and ALT levels and ii) to stratify the individual risk of these children to have liver injury on the basis of this gene-environment interaction. The gene discussed is GPT; the disease is Insulin resistance.