Metformin is the first-line treatment for type 2 diabetes (T2D) in adults, children and young people, particularly in obese or overweight patients. Many studies have demonstrated that metformin is associated with weight reduction in adults and in prevention or delay of T2D onset in those who are at increased risk. In 2012, metformin was recommended by the UK National Institute for Health and Care Excellence as a treatment option in adults aged 18 years or over, who remain at high risk of T2D, despite participation in an intensive lifestyle-change programme. Prevalence of childhood obesity is increasing and is associated with elevated long-term risk of T2D and other adverse cardio-metabolic events; however, consensus is lacking on intervention strategies aimed at reducing this risk. This article discusses the rationale and evidence for the use of metformin in obese children and young people at high risk of T2D. © Springer International Publishing 2013.