Abstract This paper describes the current prevalence and time trends of childhood obesity worldwide, and the association between childhood obesity and socio-economic status (SES). Childhood obesity has become a global public health crisis. The prevalence is highest in western and industrialized countries, but still low in some developing countries. The prevalence also varies by age and gender. The WHO Americas and eastern Mediterranean regions had higher prevalence of overweight and obesity (30-40%) than the European (20-30%), south-east Asian, western Pacific, and African regions (10-20% in the latter three). A total of 43 million children (35 million in developing countries) were estimated to be overweight or obese; 92 million were at risk of overweight in 2010. The global overweight and obesity prevalence has increased dramatically since 1990, for example in preschool-age children, from approximately 4% in 1990 to 7% in 2010. If this trend continues, the prevalence may reach 9% or 60 million people in 2020. The obesity-SES association varies by gender, age, and country. In general, SES groups with greater access to energy-dense diets (low-SES in industrialized countries and high-SES in developing countries) are at increased risk of being obese than their counterparts.