Childhood obesity has reached epidemic proportions and its prevalence continues to rise, even among very young children. A recent report from the National Health and Nutrition Examination Survey (NHANES) revealed that from 1999 to 2002, 10.3% of children ages 2 to 5 were overweight, an increase from 7% in 1994. Epidemiologic evidence is now emerging that suggests obesity in childhood and adulthood may often originate from accelerated weight gain during infancy. Further data are accumulating that link short sleep duration with obesity during childhood and later life. Prospective data are lacking that demonstrate whether the accelerated weight gain during infancy can be prevented and whether interventions to improve sleep early in life can prevent childhood obesity.