Primary childhood obesity has reached epidemic levels in industrialized countries particularly in North America. Twenty five percent of children and adolescents in the United States are overweight and 14% are obese. However, the prevalence of obesity is alarmingly rising in other less developed parts of the world, like Asia, the Middle East and some parts of Africa. Overweight and obesity in childhood extend to adulthood and the majority of obese children grew as obese adults. Obesity has significant impact on both physical and psychological health with serious consequences. The mechanism of development of obesity is not fully understood, and it is believed to be a disorder with multiple causes. Genes are pivotal but, diet and lifestyle preferences, and environmental factors are equally important. There is supporting evidence that excessive intake of sugar-rich soft drink, increased portion size, and steady decline in physical activity have been playing major roles in the current obesity epidemic worldwide. Prevention, not treatment, is the key strategy for controlling childhood obesity. It may be achieved through interventions targeting built environment, physical activity, and diet. This article covers the epidemiologic and clinical aspects of this condition.