For prevention of obesity in the Chinese population, it is necessary to define the optimal range of healthy weight and the appropriate cut-off points of body mass index (BMI) and waist circumference for Chinese adults. The Working Group on Obesity in China under the support of the International Life Sciences Institute Focal Point in China organized a meta-analysis on the relationship between BMI, waist circumference and risk factors of related chronic diseases (e.g., high diabetes, diabetes mellitus, and lipoprotein disorders). Thirteen population studies in all met the criteria for enrolment, with data of 239 972 adults (20-70 years of age) surveyed in the 1990s. Data on waist circumference was available for 111 411 persons, and data on serum lipids and glucose were available for more than 80 000. The study populations were located in 21 provinces, municipalities and autonomous regions in mainland China as well as in Taiwan. Each enrolled study provided data according to a common protocol and uniform format. The Center for Data Management in the Department of Epidemiology, Fu Wai Hospital, was responsible for the statistical analysis. The prevalence of hypertension, diabetes, dyslipidemia and clustering of risk factors all increased with increasing levels of BMI or waist circumference. A BMI of 24 with best sensitivity and specificity for identification of the risk factors was recommended as the cut-off point for overweight; a BMI of 28, which may identify the risk factors with specificity around 90%, was recommended as the cut-off point for obesity. A waist circumference over 85 cm for men and over 80 cm for women were recommended as the cut-off points for central obesity. Analysis of a population-attributable risk percentage illustrated that reducing the BMI to the normal range (<24) could prevent 45-50% of the clustering of risk factors. Treatment of obese persons (BMI = 28) with drugs could prevent 15-17% of clustering of risk factors. When waist circumference is controlled at under 85 cm for men and under 80 cm for women, it could prevent 47-58% of clustering of risk factors. Based on these guidelines, a classification of overweight and obesity for Chinese adults is recommended.