When the author began her career as a paediatric endocrinologist in Los Angeles, USA, 30 years ago, childhood obesity was rare and type 2 diabetes in young people was almost unheard of. Nowadays, however, one in three children in that city is overweight or obese, and a quarter of the children diagnosed with diabetes at her centre have type 2 diabetes. This situation mirrors developments in paediatric health throughout the world; obesity and type 2 diabetes in young people are now regarded as related global epidemics.