1. Childhood obesity is increasing worldwide and is associated with an increase in cardiovascular risk factors in childhood. 2. In children, obesity is associated with hypertension, impaired vascular function, dyslipidaemia, atheroma, the metabolic syndrome, type 2 diabetes, systemic inflammation and oxidative stress. Greater risk is associated with clustering of risk factors. 3. Obesity tracks from childhood to adult life and predicts adverse levels of risk and an increase in cardiovascular end-points. 4. Adults who were obese as children have higher rates of obesity and its sequelae: greater intima-media thickness, left ventricular hypertrophy and atherosclerosis. There is greater all-cause and cardiovascular mortality, as well as a greater risk of stroke, in long-term follow-up of obese children. 5. Genetic and environmental factors contribute to familial aggregation of obesity, with parental obesity as a strong predictor of obesity in children. However, clustering of adverse health-related behaviours is seen in such families. 6. Adverse behaviours (smoking, poor dietary choices, less physical activity and greater alcohol intake) also cluster in individuals, suggesting the need for multimodal interventions. 7. Recognition of families at risk offers opportunities for prevention of obesity in children and decreasing risk in parents.