Obesity is the most prevalent nutritional problem in the United States. It appears that both the prevalence and severity of obesity have been increasing in recent years. Obesity often begins in childhood and has a number of severe sequelae, including non insulin dependent diabetes mellitus and cardiovascular disease. Unfortunately, obesity is very resistant to treatment. This places a premium on prevention. However, the identification of clinically useful predictors of obesity which are present prior to the onset of excess weight gain has been problematic. Recently, it has been shown that the timing of body mass index (BMI) rebound may be a predictor of future obesity. BMI increases during the first year of life. It then declines until it reaches a minimum value during childhood and subsequently increases into adolescence and adulthood. The nadir of BMI is called BMI rebound. Studies have shown that BMI rebound at a young age is associated with increased risk of obesity later in life. Currently, very little is known about the epidemiology of BMI rebound.