The prevalence of obesity in childhood has been increasing dramatically worldwide in recent years. It is associated with cardiovascular disease, hypertension, diabetes, osteoarthritis and cancer (Hannon et al 2005, Nathan and Moran 2008). Children who are obese also have an increased risk of obesity persisting into adult life; in addition, obesity in childhood has also been associated with mental health issues in young people (Gray and Leyland 2012). While the measurement of obesity in adults can be calculated easily using body mass index, determining overweight and obesity in children is more controversial (Griffiths et al 2012). This article explores the tools and strategies used to measure and assess overweight and obesity in children and determine what is currently considered to be the most reliable and effective.