High body fatness, overweight and obesity in childhood are a major UK health challenge. However, body mass index (BMI), the most widely used marker of childhood body fatness, based on weight and height, is very inaccurate. This project will identify more accurate markers of body fatness in children, which are based on simple non-invasive measurements and are also associated with early markers of diabetes and cardiovascular risk. Initial identification of novel body fat markers will use a range of approaches, including (i) using measurements of weight and height more accurately; (ii) using other body build measurements (particularly waist circumference and skinfold thickness) and (iii) using bioelectrical impedance measurements. These approaches will be tested in pooled data from four studies with `gold standard’ body composition measures in children of White, Black and South Asian ethnicity. The cross-sectional associations between novel body fat markers identified in this first stage and early markers of cardiovascular disease and type 2 diabetes risks in childhood and adolescence will then be studied in independent data sets including ALSPAC, to see whether the associations are stronger than those for conventional body fatness markers, particularly BMI.