Obesity in adults is associated with excess mortality and excess risk of coronary heart disease, hypertension, hyperlipidemia, diabetes, gallbladder disease, certain cancers, and osteoarthritis. Overweight children often become overweight adults, and overweight in adulthood is a health risk. Although childhood overweight may not always result in excess adult health risk, immediate consequences of overweight in childhood are psychosocial and also include cardiovascular risk factors such as hypertension, high cholesterol, and abnormal glucose tolerance. The causes of obesity are poorly understood, and both the prevention and the treatment of obesity are difficult. In this context, the ability to track epidemiologic trends in overweight and obesity is important.