<b><i>Objective:</i></b> Childhood obesity has become epidemic and has been accompanied by an increase in prevalence of type 2 diabetes (T2DM) in youth. Addressing obesity and insulin resistance by drug treatment represents a rational strategy for the prevention of T2DM. A systematic review was performed to evaluate the effectiveness of metformin in reducing weight and ameliorating insulin resistance in obese nondiabetic children. <b><i>Methods:</i></b> A PubMed database search was conducted, using ‘metformin', ‘obesity', ‘insulin resistance', ‘children', ‘adolescents' as search terms. <b><i>Results:</i></b> Eleven trials were included in the present review. Metformin was administered for 6-12 months at a dosage of 1,000-2,000 mg/daily, decreasing BMI by 1.1-2.7 compared with placebo or lifestyle intervention alone. Concomitantly, fasting insulin resistance improved after metformin therapy. Posttreatment follow-up was performed in one study, showing that after 1 year of discontinuation of therapy the decrease in BMI disappears. <b><i>Conclusions:</i></b> Short-term metformin treatment appears to moderately affect weight reduction in severely obese children and adolescents, with a concomitant improvement in fasting insulin sensitivity. Further studies with longer treatment period are needed to establish how much metformin can reduce weight and its real utility in preventing T2DM development in pediatric patients.