Background: The raising prevalence of childhood obesity is becoming a major public health concern in many countries, but little is known about the prevalence of childhood obesity in China. This study was undertaken to establish a screening standard for body mass index (BMI) in Chinese school children and adolescents on the basis of data obtained from different geographic regions and populations.

Methods: The data were obtained from 228 250 students aged 6 to 18 years who had participated in the 2000 National Surveillance Program on Students' Health and Physical Fitness, China. Analysis was made between groups of students from different geographic regions, from urban and rural areas, and from regions with different socioeconomic development. The percentiles of 5%, 50% and 95% were calculated and compared.

Results: Differences in BMI between the various groups were seen in the percentile of 95%. The BMI on the percentile of 95% for 13-year-old boys was 25.7 in the group from large and developed cities, compared with 21.1 for peers living in underdeveloped rural areas. The corresponding figures for girls were 22.8 in urban and 20.8 in rural areas. Significant geographical north-south differences were found, particularly during the adolescent growth spurt. Among 11-year-old girls, the average BMI was 22.3 in north and 21.0 in south China, whereas in 14-year-old boys the average BMI was 25.4 in the north and 23.5 in the south. The results of this study showed clearly that obesity is particularly prevalent in the metropolitan areas and in north China. Significant differences in BMI between developed and developing areas are already visible in primary school children. Differences in BMI on the percentile of 5% were less pronounced, showing that malnutrition and underweight are still prevalent in all subgroups.

Conclusions: As the national criteria for obesity screening in China, a reference group from developed metropolitan areas may best reflect the current situation and may also represent the general tendency of develop-ment. However, significant rural-urban and north-south differences exist along with gross inequalities in terms of material living standards, which should be taken into consideration.