To develop an internationally acceptable definition of child overweight and obesity, specifying the measurement, the reference population, and the age and sex specific cut off points. International survey of six large nationally representative cross sectional growth studies. Brazil, Great Britain, Hong Kong, the Netherlands, Singapore, and the United States. 97 876 males and 94 851 females from birth to 25 years of age. Body mass index (weight/height(2)). For each of the surveys, centile curves were drawn that at age 18 years passed through the widely used cut off points of 25 and 30 kg/m(2) for adult overweight and obesity. The resulting curves were averaged to provide age and sex specific cut off points from 2-18 years. The proposed cut off points, which are less arbitrary and more internationally based than current alternatives, should help to provide internationally comparable prevalence rates of overweight and obesity in children.