Research suggests that children who reach puberty early are at risk of poorer health and wellbeing. Such ‘early maturing’ children also tend to take part in riskier health behaviours, such as smoking, drinking alcohol and risky sexual activity. However, most studies look at these links at a single point in time, which limits how confident we can be that early maturing causes poorer wellbeing. Few studies have looked at what factors may increase or decrease some of these risks. Our study aims to use the ALSPAC data explore three questions relating to the longer-term health risks of adolescents who mature early. The first builds on work we have done with parents, showing many believe we should judge whether or not a child is overweight differently if they are an early maturer, to avoid labeling them as overweight when they are not. This is a particularly important time to consider how we respond to children's weights, as it is the point at which over 95% of children in England are weighed and measured as part of the National Child Measurement Programme. Some parents have been strong critics of this process, so public health teams and parents alike are interested in exploring how we could interpret and use this information better. To explore whether it is appropriate to use the same means of classifying early and on-time maturers as overweight, we will apply an adjustment for maturity to our calculations of weight status for children at age 11, and explore whether this is a better way of predicting which children will have higher/lower future health risks at age 17 (including obesity, blood pressure and other risk factors). Second, we will compare which factor at at age 10/11 is the stronger predictor of wellbeing in later adolescence; being overweight, or maturing early. Finally, to explore what factors might help children to avoid some of the potential consequences of maturing early, we will look at whether children’s views of the strength and importance of their relationships with parents and peers influence the effect of being an early maturer on their wellbeing by the age of 17 (including depression, positive wellbeing, and risk behaviours such as smoking and drinking).