Obesity is a well-known contributor to type 2 diabetes, cardiovascular disease, disability and premature death.  Joyce Lee, from the University of Michigan Health System (Michigan, USA), and colleagues studied 8157 adolescents and young adults, ages 14 to 21 years at the start of the National Longitudinal Survey of Youth 1979.  The researchers found that the measure of degree and duration of excess weight (based on the number of years body mass index, a calculation of weight and height, of 25 or higher) was a better predictor of diabetes risk than a single measurement of excess weight.  The team urges obesity prevention and treatment efforts that focus on adolescents and young adults, and suggest that measuring and following BMI and the cumulative "dose" of excess BMI among adolescents and young adults may be helpful for clinicians and patients in understanding risk of diabetes in the future.