There is a worldwide increase of overweight and obesity not only in adults, but also in children. Data used to estimate prevalence are, however, collected in differing age groups using nonstandardized measurements and instruments and refer to differing time periods. Moreover, various reference systems to classify overweight and obesity exist, thus, adding to the difficulty in comparing countries. In this paper, these problems are discussed in detail. The most common reference systems are introduced, and their impact on the estimation of the prevalence of overweight and obesity is demonstrated. Based on available data of the global situation, maps that depict the worldwide distribution of the prevalence of overweight and obesity in children and adolescents are presented. Finally, these maps will be discussed critically. Although it may be assumed that these data are collected according to the best quality standards available, the lack of a unified protocol to conduct studies on childhood obesity hampers the comparability of data between countries. Obvious limitations in that respect are the use of different reference systems, differing sampling schemes, and differing age groups. More subtle limitations result from, e.g., different measurement methods, including self-reported weight and height.