The severity and frequency of childhood obesity has increased significantly over the past three to four decades. The health effects of increased body mass index as a child may significantly impact obese youth as they age. However, many of the long-term outcomes of childhood obesity have yet to be studied. This article examines the currently available longitudinal data evaluating the effects of childhood obesity on adult outcomes. Consequences of obesity include an increased risk of developing the metabolic syndrome, cardiovascular disease, type 2 diabetes and its associated retinal and renal complications, nonalcoholic fatty liver disease, obstructive sleep apnea, polycystic ovarian syndrome, infertility, asthma, orthopedic complications, psychiatric disease, and increased rates of cancer, among others. These disorders can start as early as childhood, and such early onset increases the likelihood of early morbidity and mortality. Being obese as a child also increases the likelihood of being obese as an adult, and obesity in adulthood also leads to obesity-related complications. This review outlines the evidence for childhood obesity as a predictor of adult obesity and obesity-related disorders, thereby emphasizing the importance of early intervention to prevent the onset of obesity in childhood.